Board Thread:Questions and Answers/@comment-30388913-20170215173614/@comment-30708811-20171221042444

Evilwizard89013 wrote: They don't necessary fuse possession means they can host a person or thing so that Bering said he also manages to survive acid rain from napstablook he also says at the end of his fight that neither frisk or mad dummy could hurt each other due to him being unarmed and out of minions and the protagonist being a pacifist.

So I think that his soul either dematirialized in a science killing him or he went into an eternal limbo of fear

You guys can vote on which one you think is more probable Whenen they are corporeal, they do fuse  and therefore can die. If he stayed incorporeal, the dummy shell would be destroyed and he would go looking for a new host.