Hi you know I don’t see it as you owing them anything. It’s certainly not your fault of course and nothing that you can do about it. But it is a major inconvenience and bummer for their trip, huh? I would see it as maybe something nice to do for them — either discount their affected night(s) or if you’re close take over lots of electric candles, ice, and maybe a meal card to a local restaurant since the kitchen is affected. If I were the guest I wouldn’t really expect it, it I would see it as a very hospitable and fair thing if you reached out in nice ways to make their trip happier.