Board Thread:General Discussion/@comment-30640746-20170406110954/@comment-13682699-20170409153102

Its unknown whether anything happens to a soul after it leaves the "mortal coil". They probably believe similar things about heaven/hell type of afterlife similar to humans because when Flowey talks about how he first learned about resets and that he tried to kill himself at one point, he mentions that as he was leaving the mortal coil, he became afraid of what would happen to a person without a soul or if he would be able to pass on like other souls. This implies that monsters likely believe in some sort of afterlife just like most humans do.

Also, when a SOUL resets, it actually does reset their timeline because they aren't just 'brought to life' after a reset. They move back in time to the point where they first acquired the RESET ability.