Why is Bill Cipher considered Presumed Deceased?

I know he said he could return in that reversed statement before Stanley defeated him. But Stan punched him into oblivion in the FINAL episode of the series. I personally think a fate like that in the finale would confirm death. But please, tell me what you think.

Jester of chaos·7/9/2020

One book implied that the canon secret is when he said that it would indeed happen and then the incantation in the show. It’s left with some debate especially when it sends with a shot of Bill’s body and then a scavenger hunt which will not canon gives the indication he still exists.

Geek from Hell·7/9/2020

I don't maybe of this:

https://youtu.be/hGACwJmYres

Bill Cipher's Backwards Death MessageYouTube

What do you think?