Gatwick Express Closures Christmas / New Years...suggestions?

We took a car service to Gatwick from Mayfair and I would be hesitant to do it again. I can’t recall the vendor or the cost. We made good time (and this was at 5AM or so) but he said that’s the exception. He said traffic can be very bad and he’s had rides that took 2 hours plus. Just to make me even more nervous he stopped for petrol and candy bars! I think your idea of an Uber to the train is a better one.

Take the bus from Victoria Station at 4 am; It takes an hour and currently cost 10 pounds
National Express][1

The Gatwick Express closure doesn't really come into it, as your journey would be quicker via Thameslink anyway. It is how early you want to get to Gatwick, starting from north London.

Have you considered walking or taking a cab to Kentish Town and taking the train from there?

The car route would ether be a great way round via the north circular/M25, or by threading through the centre. Either way would likely be a little longer than the public transport option although you do have an early start on your side which might equalise things.

There is an amended timetable on Thameslink on the 27th due to engineering works in the Kentish Town area. I don't know if Kentish Town station would be affected, but if you have luggage Kentish Town wouldn't be my station of choice. There are narrow walkways at the top, and narrow steep stairs down to the platform. My memory (I go there for burritos) is that there are no lifts.

Victoria is shut for engineering works all that week so no Southern services from Victoria to Gatwick either.

There is no suitable train from Kentish Town to get to Gatwick in time.

The earliest from Blackfriars is 05:29 Gatwick 06:04 direct. Earlier involve a walk to London Bridge and you don't want that.

The earliest from London Bridge is the 05:14 for 6:00 at Gatwick direct.

The trains are normally 24 hours on that line - but it is Christmas and the elves who have been delivering presents need work to do so they play on the trains until New Year.

If you have the money take the car is my advice. Otherwise it is a car to Blackfriars or London Bridge, take the first train of the day, and hope. I worked on the trains for many years and I wouldn't want to do that.

Take the car. Hopefully you can afford it.

Accepting there is a late or restricted start on Thameslink, TfL is late in reflecting it. Although they are often very slow in updating info for services they don't run themselves.

If it were me I wouldn't be happy with relying on what is bound to be stretched services early in the day, with few backstops to meet the flight.

Don't suppose there is a chance of leaving your London lodgings a day early and spending the night at an airport hotel?

You'll still be getting up early, but not at stupid o'clock like you will from North London.

I've never taken a minicab (Brit-speak for a car service), but three that are often recommended are

Blackberry Cars http://www.blackberrycars.com/
Simply Airports http://www.simplyairports.co.uk/
Just Airport https://justairports.com/

If you go to their websites and put in all your details (size of car, exact address, cash or credit card payment, etc), you can get a price quote from your lodging to Gatwick. You can then decide if you want to do this, or use Nigel's idea of an airport hotel the night before.

Thank you so very much everyone for your helpful suggestions!
Looks like a private car is the best bet for us...fingers crossed. I don't know what I was thinking booking a 7:15 AM flight...