The plan was good. Perfect, even.
All he had to do was return to the past and tell Alvin what would happen in the future of this timeline.
Then, using the "Time Heist" device, he could travel to "Endgame" and defeat the Kree Empire, which had already been corrupted by Slaanesh. That would rewrite the future timeline and open up a parallel world!
But after hearing the plan, Peter froze.
Like a lonely child, he stared blankly at Pym, confusion in his eyes, and asked softly, "Then... what about this world?"
Pym's heart lurched. He lowered his head, unable to meet Peter's eyes.
Suddenly, he felt consumed by guilt.
"That's only one possibility, son." He did not know how to explain it, so he could only tell the truth. "If we want to change the future, we'll have to make choices in the past. According to our current theoretical knowledge, altering the past might create a new branch of time, or it might not... nobody knows what will happen."
Alvin's appearance had already changed the "past," creating a new worldline in the future.
Killing him would not change the "facts" that had already come to pass.
That left only one option: reverse the Avengers' defeat in the "future that was no longer the future"-in other words, "Endgame." Perhaps that would create a new worldline. Perhaps it would change the existing future.
Either way, at least one "future" would have an Earth that had not fallen, that had not become a nest of Daemons.
But for a boy who had held on alone for two years in the apocalypse, that outcome was a little too cruel!
"So, no matter what happens, at least one future will be saved, right?" Peter closed his eyes, took a deep breath, then smiled. "All right.