JOHN AND DAVE DIE IN THE LAST BATTLE OF THE GAME, SO IT TAKES PITY ON THEM AND CREATES A FALSE UNIVERSE WHERE THEY CAN MEET AND LEAD NORMAL LIVES
ONLY THEY DON’T KNOW EACH OTHER AND THEY MEET IN SOME STUPID COFFEE HOUSE AND THEY BEGIN AS FRIENDS AND AS THEY GET CLOSER THEY GET MARRIED AND ADOPT A CHILD AND JOHN NAMES HER CASEY AND DAVE TOTALLY AGREES BECAUSE ITS FOR IRONIC REASONS. AND THEN CASEY GROWS UP AND JOHN AND DAVE GET OLDER and live out their lives joking and even as an older man john is playing pranks on dave and dave is still totally done with them but still still loves john no matter what
and then john dies of old age
and soon after dave follows suit because a life without john isnt one worth living
and then as if seconds had passed they are revived back into the final boss level and only then do they realize what the game had shown them
(continuation of that john, dave, and karkat comic)
Obviously Dave was about to come out to John, and John realized what Dave was trying to say. Unfortunately, John had planned to prank Dave and Karkat and had already pulled the lever to release the Faygo. He tried to undo it, but became frustrated and broke the lever. Now we know how that ends.