I'm going against the prevailing opinion to say that I have sympathy with your friends - we pulled out of a gite in France (going with my parents, although we all agreed to do so) the day before the final balance was due, because of the imposition of quarantine. I was devastated as this was a cancelled 2020 holiday, booked in 2017 to celebrate my mother's 70th.
Travel rules are changing almost daily - in fact, according to the papers, Spain and Greece may go to amber plus whilst France goes back to amber - if that happens next week we would have been able to go. However, the stress of the tests, the paperwork and the chance that even if we changed our rules, France may change theirs whilst we were away meant that we all decided to just cancel. Fortunately, the gite owners have been fantastic throughout and totally sympathetic to our situation. On Friday evening, France imposed a rule that minors over 12 now have to be tested, even if travelling with double vaccinated adults - my friend had to move her holiday at the 11th hour as they were due to go at 5am on the Saturday.....travelling anywhere currently is a risk, and if they weren't prepared to take it, then I think that in the middle of a pandemic, that is their prerogative.
I would definitely try the owners of the villa - some money is better than no money and they may offer it to you at a reduced rate.