@dorothy there is not that much you can do, even more so as it is not your bounty, but a bounty on your question. It is in theory possible for moderators to cancel a bounty. This is generally something that is rarely done.
To come back to the original question what you could do: you could still flag the post or the answer for moderators attention. Using flag, "other" and explain the situation. This would be private.
Yes mainly I answer number theory here.
It is not clear what if anything moderators could or would do but there is not that much else to be done. This is a bit of a drawback of the bounty system but various aspects needed to be balanced.
The question seems alright; I did not look in detail though. Sorry I have to leave now. Actual work is calling. It was nice talking to you @dorothy Hope the bounty situation will get resolved. There are still two days, perhaps a better answer will emerge.
quid, feel you are making some assumption re grothendieck fields medal. agreed there are some differing accts in the media. have not yet found more clear details of his "acceptance" or "rejection" of the prize. he is known to have rejected another prize worth far more money. he is listed on the Fields medal prize page with a "cross" next to his name where nobody else has that cross. wonder what the cross means?
it is now a case that math awards are sometimes "given/ awarded" even if they are not "accepted". eg perelman iirc.
the rejection of the prize is noted in my blog because it strongly attests to grothendieck's... to put it lightly... "eccentricity".