A few unhappy endings that an audience wouldn't like that would turn Good Will Hunting from a comedy to something else are Matt Damon doesn't go to California to look for the girl, she cries inconsolable for a short while, then marries another guy, while Matt Damon stays in Boston going to Little League games long enough for Ben Affleck to follow through on his promise of killing him (a fact and not a threat in his words). Ben Affleck would think he was doing the world a favor, kind of like the Of Mice and Men story, and puts a bullet in the back of his head down by the river, dropping his body to the bottom. Another possibility Robin Williams provided was for Matt Damon to become another unabomber, perhaps he puts a bomb in the mailbox for Skylar's husband to open, but instead of him being the one to check the mail that day, Skylar is disfigured forever or killed by the bomb when she opens the mailbox, and Matt Damon has to live with that for the rest of his life. There's more possibilities than just those two that nobody explored.