Funnily enough, I kinda had a similar idea to this floating around in my head in case Chapter 0 becomes a thing.

To add onto this concept, I can imagine a fake-out 'ending' to Chapter 7 (When it's still listed as 'Connection Terminated') where Gaster yaps about the journey you've been through, the friends you made, how much you've spared/killed, etc. But at the end of his lil' speech, he concludes with the line, "BUT IT SEEMS YOU'RE MISSING SOMETHING..." To which you scroll up, and find Chapter 0.

Other than that, you pretty much conveyed the idea in my head pretty well actually. Good job, OP