london/paris question

relying on Eurostar usually can be successful, but things do happen. French train strikes (this weekend), English train strikes, incidents on the line, sometimes, incidents between arrival in London and the airport.

Not often, but sometimes.

If such were to cause you to miss your plane, what's the worst that could happen?

If you are in London the day before you could mitigate against them, and if you fly home from Paris you mitigate against them completely.

it comes down to how brave (or not) are you?

What Nigel said.

Call Virgin. They don't fly out of Paris but might be able to put you on one of their alliance partners like Delta or Air France. It will cost you.

It might be cheaper to just take the Eurostar or a flight to return to London the day before. Price this first then call Virgin so you can compare prices.

If that doesn’t work, go to Paris first.

I do this a lot, because I find cheaper fares to London than any place else, and I like to go to Paris. I would never do it the day of, I once had a situation where the trains out of Paris were delayed for five hours, and there was a woman there sobbing because she was going to miss her flight home at Heathrow. I was going back to London to go home the next day so I had 24 hours to deal with the problem. And I did wind up rebooking a train through Brussels just because it was such chaos.

But if you miss that flight back home, it’s on you and the airline does not have to do anything

We have done the London / Paris combo multiple times, always rely on Eurostar, and we have an open jaw flight schedule from the US via LHR and CDG. Our favorite way to do this combo is we fly to Paris first - then at some point Eurostar to London - then London to US, and whichever order we do the cities, we have not and would never count on Eurostar for a same day transfer from either city to catch a flight home as you first asked about. So our Eurostar trip always take place somewhere in the middle of our trip abroad, allowing for disruptions that, while a nuisance, have nothing to do with missing a transatlantic flight connection and being on the hook for that cost.

So given that you already have your roundtrip air to/from LHR, plan to return to London at least one day prior to your LHR flight home. For future reference, open jaw is the way to go, though. While taking the Eurostar is a nifty way to connect between London and Paris (or vice versa), I would not rely on it for a round trip connection myself given the vagaries of train strikes and other disruptions.

All else being equal, I prefer taking the Eurostar FROM Paris to London rather than the other way around. Why? Getting to the station and processing through security seems easier / less hassled in Paris, for one thing, and I also find getting to LHR from central London for a return flight home is "easier" than getting out to CDG from central Paris on the morning of a flight home. These are personal preferences, but they are based on having done this many times before, so YMMV...

Would we be okay to take an early train back from Paris in time to make it to LHR from St Pancras?

It is theoretically possible, but not a risk I would take.

Or should i see if Virgin will let us switch and fly out of Paris back home?

Virgin does show CDG-LHR-USA itineraries, using Air France for the CDG-LHR leg.

You can ask and see if the cost is acceptable.

If you must fly r/t LHR, then the solution I would do would be to spend the 1st night in London, go to Paris the 2nd day and then go back to London for the balance of your time. An overnight flight to London and then on to Paris the same day by train looks to be a really LONG day. Me, I would be labeled 'road kill' the following day.