How much of this money do I stand to lose?

I doubt that anyone can give you any kind of estimate without knowing the refund policies of the companies you booked with for each part of the trip, and whether or not the activity is cancelled by you or them. Did you get any trip cancellation insurance? The airfares may be refunded if the flights are still cancelled, otherwise you may just get a voucher for a future flight.

I would look at the cancellation policies for each piece and then based on those determine what your next steps should be. The trip isn't until July and there is every reason to believe the world will have returned to normal by then.

That was my impression too Nancy but there's a lot of posters in this forum stating forget any kind of international travel in 2020. But yes I'm waiting for now until late May.

Here's what I'm looking at for my to be canceled trip with my wife. The airlines will allow one free change to be used up to one year from the time I bought the tickets. All the booking.com reservations I made are free to cancel. The insurance will not cover the airline tickets because the pandemic was noted on Feb. 8 and it doesn't matter when you bought the tickets for that. However if we are too sick to travel then we can apply for a canceled trip. So I am going to let the airlines cancel my trip and they will give me a voucher to be used before the time of one year of when I bought the tickets. This is my situation yours might be different. Good luck!! There are lots of people feeling the pain, don't let it get you down. Also I can use my travel insurance for another trip within 700+ days!

If non-refundable, wait for cancellation and then get a refund. If you cancel early, then you may miss out on full refund.

The trip isn't until July and there is every reason to believe the
world will have returned to normal by then.

What is the evidence (or at least a reasonable hypothesis based on some measurable indicators) behind this bold assertion?

To the OP - everything depends on your cancellation policies with every vendor/ provider and how much flexibility you have with potential credits for future travel. No one here can speak for any vendor you cited - the contract is between you and them.

Joe: The airlines won't charge you a "change fee" but they WILL charge you the difference between your old fare and your new one. If you want to support hotels - then cancel your booking.com reservations and book directly with the hotels. Why should they have to pay commission to booking.com when they offer the exact same thing or maybe even a BETTER price?

Tim, I book with Booking.com because they quite often offer a better deal of when to cancel, they are more secure on the internet, and they are easier to book. Anyway it works for me with less hassle.

What a mess guys. Been planning this thing for do long and looking forward to it. I think the loss of the opportunity to go hurts more than the financial part.

The trip isn't until July and there is every reason to believe the world will have returned to normal by then

July of what year?

Maybe July 2021 in a best-case scenario if we get lucky. If you are following scientific experts, July 2022 looks more likely for "returned to normal" (or something like it).

More to the OP's point: I'd stop worrying about the exact dollar figure that you may lose in costs for this trip. Because it's impossible for anyone to know right now. And because everyone (perhaps everyone in the world) is going to lose a lot in this pandemic, nobody reading this is is going to be spared. July (of this year) is a lifetime away in pandemic-time. You won't really know about refund policies until June. If you spend the next 3-4 months worrying about exactly how much you are going to be out-of-pocket because of all this, you will go crazy. Let it go for a while. You'll know more about the financial hit you will take for this trip in a few months, but you probably won't be able to do anything about that for quite a while (and, frankly, some folks might say there are more important things to worry about). Regardless of your priorities, there's little or nothing you can do about it now, so there's no need to drive yourself crazy over details. Just my 2 cents.

Yes, check the Terms and Conditions of you booking. If you have a non-refundable (no cancellation) booking, be prepared to use it or write it off. I had three Expedia no cancellation discounted Milan bookings. If I canceled, I would not get a refund or credit. However, my the Hotel Berna shutdown because of the lockdown before the start of my 5 night stay. Expedia contracted me (numerous times including voice messages and e-mail) offering to find me alternative accommodations or full refund. I chose the full refund for the 5 nights and Expedia credited my credit card account within a day. Lesson learned is don't cancel a non-refundable and you may get lucky. But that said, be prepared to write-off non-refundable bookings.

I'm sorry to hear that your trip likely could be affected by the pandemic. Money aside, it is the disappointment that is involved. Although international travel not being a part of our trip, we had to cancel a trip that was many months in the planning. We had planned a family girls trip to NOLA in two weeks. It took much effort to coordinate 7 schedules of those coming from 6 states to be together for the first time in 23 years. Sad as we all are, it isn't worth the risk.

As to my "bold" assertion - two points: one, it's based on studies I have read and two: I am an optimist.

Please share any study links. I'm sure readers here would like to feel more optimistic. I'm looking at the Johns Hopkins data daily and the trajectory is not positive in terms of number of cases and deaths. It took China about 3 months just to begin to turn the corner, and it used very strong authoritative measures to do so. The rest of the world may not have these levers.
https://coronavirus.jhu.edu/map.html

Hello Agnes - since the studies aren't truly travel related, this isn't probably the right forum for that. What I will say is this - this is about data and although what we have is not as extensive as we'd like, taken as a whole nothing I've read suggests that this is indeed a pandemic of the century. Locking down the entire world for months on end simply isn't feasible - we will and must shift from risk avoidance to risk management and I think we are trying to figure out how to do just that.
Now, do I think that all areas of the world will be fully open for business as usual - probably not (due to a whole host of reasons) but on the other hand, I don't expect that the entire world will remain shuttered either.
As for travel planning (or adjusting those travel plans) obviously, everyone needs to look at their arrangements and learn what the options are for cancellation. To the extent that it's a "cancel now or cancel later ,the result is the same" - I'd personally wait and see since I could always cancel at a later time based on circumstances on the ground. If the cancellation requirements are more along the lines of "the longer you wait the more you will lose" - that's a trickier one and will really be up to each individual's tolerance for risk and uncertainty and as such, no advice is really possible.
Finally, I am optimistic because IMO the world has faced much larger challenges and triumphed and I am confident we will overcome this as well.

I would caution against using China as a timing model. China, once the government acknowledged the COV-19 theat, took decisive action locking down Wuhan. Recent Business Insider report has Wuhan scheduled to reopen April 8. In contrast, the US is only shutting down state by state as governors take action and the president is hoping to reopen the country in two weeks (by Easter).

Why not ride this out? If they become the ones cancelling, you have better options. But, as said, it all depends on your purchase terms of agreement. Yes, it is stressful waiting, but Europe is going to need tourist dollars by this summer. As long as your state population doesn't get bored and non compliant, I would think there is a good chance you can do this trip.
If you start cancelling, you are bound to lose a good amount.
Right now, assess all your terms of purchase for current cancellation options. If your hotels hsve 'free cancellation', write down the last date you can cancel. Unlike the US, these are not all 24 or 48 hours prior. Some may be 2 - 4 weeks prior to arrival. If you have to commit too far in advance, consider shopping for an alternative with a cancellation date closer to arrival date. If they are non cancellable, then you most likely can kiss those good bye...particularly if you try to cancel too soon. If Greece is in lock down late May, read Booking's COVID statement. Maybe they could be salvaged.
To be honest, I would wait to cancel until 3 or 4 weeks before...unless it is clear that Armageddon has arrived and either US or Greece are in total shut down...or there are extenuating circumstances that make it absolutely necessary.

Joe - which travel insurance did you use?
I have a similar situation, but my trip is less money. My big heartbreak is that it is our second time trying to take the same trip because 5 days before our trip last year, my BF had a major work accident and we had to cancel everything. Short story = no refund for flight or direct hotel reservations, 50% refund from Rick, and full refund for Booking.com because we had no travel insurance. (I know, I know but it's our first trip and we were naiive.)
We booked our July trip in January and just bought our plane tickets a couple weeks ago (days before the world shut down). Missing the last trip was a heartbreaker. Rafimando, I am like you - feeling anxious about the next couple months, but trying to stay hopeful. At this point, I am just trying to decide if I need to go ahead with basic trip insurance or wait and see if it all gets cancelled anyway. As I have another big domestic trip planned for December, a year's worth a travel insurance would be a good idea.

From what I understand travel insurance would not really help in these circumstances unless you bought the super premium "cancel for any reason" travel insurance.

Chase Sapphire Rewards just sent us an email regarding our April hotel reservation, saying that even non-refundable reservations could be canceled without penalty . We had rooms booked with points, some refundable, one not, and the points were all returned to our account within minutes.

Rafimando, if you look at your booking.com page, on their App, then click on the suitcase in the upper right, and it should show the terms of cancellation for each of your reservations. I had to cancel my lengthy trip to Italy in April-May, mostly reservations through Booking.com. Two were non-refundable, the rest could be cancelled for free from 1 to 15 days before arrival. I called the Booking.com toll-free number, and the customer rep was very helpful. She cancelled each of those she could on her computer, and I could watch each get cancelled on mine. She phoned one of the non-refundable hotels with 24-hour desk service, and they allowed me to cancel with no penalty, given the circumstances. The final one, an agriturismo, is still pending. I’m sure every travel-related company in Europe is overwhelmed now, probably very hard to reach, especially about a July trip. Good luck.