What would happen if your self-prototyped dreamself from a doomed timeline died on your crypt bed after your "alpha" self and dream self died ? Would they become the new "alpha" you ?

Oof… Okay, self-prototyped, I’m assuming you’re talking like in Davesprite’s case. Basically you’re asking, what if Dave died and Davesprite went God Tier. And the answer is… Technically they should not be able to Ascend? Because once you go Sprite and mix with someone, you become an entity different from what you were. So the Quest Bed is yours, not theirs. Jade ascended because it was her body on her Quest Bed, and pretty much assimilated the divergent Dream Self. If it’s merely the Sprite Dream Self with no ‘self’, using your Quest Bed, I believe the difference may be notable enough to prevent Ascension.

That’s why you should Ascend to God Tier BEFORE Self-Prototyping.