Sorry to hear about the accident. It sounds like on the spot, the hotel offered to do everything that they could to help out, which is great. Unfortunately, I also agree that the compensation is now agreed, so not much to do.

I also do ultras and am interested in which 500km walk you are doing! I'm not a (useful) doctor, but I've heard that doctors can be much too conservative giving advice on sprains to endurance athletes. It depends how bad the sprain was (and if there was an actual tear), but you might be able to walk on it before that. If not, I've had "enforced tapers" before ultras work out well for me, and I showed up at the start line well rested.

Good luck!