Act 7, to my understanding

- Rings are thrown in volcano. This kickstarts the production of the new Genesis Frog.

- With the conditions for the new universe met by Echidna, the new tadpole begins to take root in the kid’s original Skaia, as shrunk, held, and then released by Jade. It travels to the center of the hole that John carved out when he extracted The Tumor, which was stopping the kid’s genesis frog from taking root. The Frog emerges, fully grown, and creates a complete new universe.

- Alt Calliope, meanwhile, destroys the Cherub’s Green Sun, and uses it’s power to create a massive, massive black hole, to destroy the old universe into the void, along with herself.

- Vriska, during the fight, deploys Caliborn’s juju, and opens it up. This creates a stable time loop that releases the kids, when they were captured by Caliborn, allowing their beings not to be tied to this universe. This switches the door they are standing in front of to the door to the new universe.

- John opens the door- through his touching the handle, everyone from their session was transported to the new Universe. Yes, everyone. Your favs are fine. (Gamzee might be there too).

- Once in the new Universe, Jade deploys Roxy’s Earth, which was the culmination of their plan- to terraform and live on that with their friends and the carapaces.

- When Lord English attacks the Juju, the door opens- on the other side. Lord English is now trapped inside.

- Using the power of the Green Sun, Alt Calliope destroys the old universe. She and everything else is gone. However, Caliborn destroying the clock means he is unkillable- and the juju is indestructible. So in the old universe, sealed in his own juju, exists Lord English. Forever quarantined to the unknowing void, floating through space.

- The last thing we see, when the kids enter, is an unprototyped kernelsprite, which signifies the circular nature of Homestuck- the “new game plus” if you will. That SBURB will return, somehow, to this new universe, and it will all begin again, eventually.

and that’s my thoughts on the matter thanks to @purplebloodedmajesty for setting this out and talking to me abt it

EDIT: please also refer to bilious-slick’s post that presents a slightly different ending but abt the same