The biggest risk is for Hauser because his contract is more important to him than it is to Boston, but he's just entering his prime, has been incredibly consistent (maintaining a strong 3p% while increasing his attempts), durable (5 total games missed in the last two seasons), and just had a very impressive playoff run in which he more than held his own on defense despite arguably the best 1v1 scorer in the league targeting him. He's the kind of guy that should be betting on himself, which is unfortunate for Boston given how expensive the rest of the roster already is.
Picking up his option likely means that Hauser turned down a team friendly extension. This isn't a surprise, nor is it evidence that he won't sign an extension at some point in the future, but it does make him less likely to accept a truly below market deal at any point, which means he's more than likely gone. Someone will absolutely overpay him, which is what happens when you can play regular rotation minutes through the playoffs while being first in both the regular season and in the playoffs in +/-.