I've just been a lurker, but I feel compelled to say this because it was revealed to me in a dream.
I believe I know what the end of the Prophecy is. It's about the three heroes having to never meet again.
Yesterday, I decided to watch Andrew Cunningham's streams. When meeting Ralsei for the first time in Castletown, if you do not run at all, he says something like “you know you can run, right?”. If you reply that you know, he says
> Really? And yet you choose not to...? Right, who knows how long these leisurely days will last... There's nothing wrong with taking your time, Kris.
It's a somewhat obscure piece of dialogue, as I've never seen it myself playing first-hand. But I think it's some slight foreshadowing to the fact that “these leisurely days” will not last for long. I was a proponent of the Prophecy ending with all the Dark Worlds disappearing, and I think this is taking that to its most extreme conclusion.
I do not think Deltarune is about escapism, but rather it's about “letting go”, about moving on: it's about finality. Let's not forget that this is also a coming of age story. “The friends you made during high school might not be there anymore, but you'll still have the memories” - that's what Don't Forget is about.
Something that also catches my attention is that Friendship - the track that plays right at the end of Ch1's Dark World, when you say 'goodbye' to everyone - very prominently features the Don't Forget motif. Considering that this is when the Lancer Fan Club's friendship is solidified, I think it has a lot of relevance.
And I think that's what the ending will be. Just like in Undertale, the game will ask you not to play it again, to let it go. And the Snowgrave route will, in part, be a reversal of that: the player doesn't want to let go, and will “freeze” the story before all the friends they've made have to depart (let's not forget that the player is also a character in-game). Though this is a bit more far-fetched imo.