I hope if they wrote a different ending in case of cancellation, it changed more than just Sean choosing to help Nick. Because while that would have at least slightly given his character the option of being redeemed in my eyes, it wouldn’t have even remotely provided closure for the series’s multiple unfinished plot threads or any of the characters, including Sean.
So…if they wrote two different endings, I hope it was more like two different last-thirty-minutes, not two different last-three-seconds.