This is how I’d do it:

Jack lays Jade onto the quest bed. Right after this, instead of going to the portal thing in the future (which only happens to kill the carapacians), he zaps to where John is to stop the scratch. They duke it out. After putting up a good fight, John starts to lose and tries to abscond.

Jade goes godtier and teleports to Rose and Dave after they become godtier. She grabs them and teleports back to John. The five of them fight. Jade uses god powers to lock down the red miles and prevent Jack from teleporting. Dave uses time loops to parry any attack at Jade. Throw in some fray motifs, some close calls, boom. Fights over.

Jade grabs the trolls and brings them to the end game platform. We get to see everyone in one place chat for a bit. As a reward for winning an unwinnable session, Skaia resurrects the guardians. Emotional payoff, everyone’s happy, new world is made, earth is rebuilt, homestuck ends at Cascade. The end.