If it were needed could AU sam grow back into his big self? Or maybe its an eventuality what with the visitor thinking of him?
hmm I think, in an extreme circumstance, Sam could resume growth! Global war, another interstellar visitor, etc. It wouldn't be pleasant. He went from a human, to something immensely huge with the sprawling mind to match, back to gutting himself down to something again somewhat-human. Regrowth would re-fracture his mind and deal a blow to his mental wellbeing, alongside whatever spurred him to regrow in the first place.
Sam's rejection of his role as Earth's protector left him with lingering guilt and distress, paired with struggling to comprehend the train of thought that led to him doing it in the first place. He'd keep up with the news (Earth's been knocked back to radio technology, with limited internet) as best as he could out of deep worry he did the "right thing".
Even a fraction of what the Visitor turned him into, he loves Earth, and his time spent as its protector isn't lost on him; he wants Earth's people to be safe and healthy, and he did the best he could before he "retired". Was this grand act of abandonment selfish? Probably. Does he still feel bad about it? Yup.
I do think it's very likely that in canon Sam grows because the Visitor never stops thinking about him (but a part of me hesitates to 100% believe it, because by extension, the Visitor never stops thinking about Earth, and nobody else on Earth seems to experience continuous mutations). But for the sake of this very self-indulgent AU, Sam wouldn't continually grow here.
