All I had booked was a day trip to Paris on Eurostar. At just £29 each way it would hardly have been a major financial disaster if I'd lost my money but they've sent me an eVoucher for the £58. I can use it to make a booking up until May next year which, since you can usually book up to 6 months in advance, actually means that it will be valid for most of next year.
However getting to St Pancras International means taking a train to London and then using the Underground, while getting around Paris means using the Metro. So even putting to one side the problems of social distancing on the Eurostar service itself, it could be hard to stay away from others for a lot of the time. Further, there's not much point in me going to Paris until I know that there will be bars, restaurants and museums open for me to visit when I get there.
So I'm not currently rushing to re-book my trip.