We agree that once we have awarded a favourite point, it stays with that cache. Although we never have a great stash of fp's in reserve (as we give them out when we can and when we get great enjoyment from a cache's hide, fun container, fabulous location etc), we do think carefully about each award and we even sometimes wish that we could give particularly great caches more than one.
Although the cache can no longer be found, if someone retracts a favourite point it has effects in the present caching world - the CO's FP's are reduced and their statistics, Badgegen etc change. This doesn't seem fair considering the effort they have probably put into making the cache which a lot of people have got enjoyment from. Also, some challenge caches depend on cumulative fp's on found caches, and if the numbers start to vary, it might affect whether someone has qualified for the challenge or not.