I have had luck and was unlucky.

It usually helps, if you are not going to fully cancel but ask them to move the non flexible stay to another date, where this rate is available as well. I always call the hotel instead of using the online system.

I was lucky to cancel two stays just a few hours after I made it (mixed up the dates) and habe been a at this hotel afew times before and after this time.

Regarding the question of the OP, in the time my grandparents were not in very good condition, I always had booked fully flexible rates - just in case.