>made Aoko truly understand the unmoving reality of life and death
Except the Magic does have the ability to revive the dead and Aoko saves Sono-G later using the same Magic.
Aoko's grandfather notes that the Magic didn't work only after it ends, so presumably in order test whether or not it'd work, he'd need to have made the exact same "immense cost" as Aoko later expends to revive Sono-G, only in this case it doesn't work why exactly? We don't actually see what happened, with Magic involved there's a ton of ambiguity for what might have occurred...
Also, I don't think it's explicitly stated that Aoko "sped up the death of the universe", rather just that she took energy from the end of the universe, and that might have some significant implications somehow. If there are significant implications to Aoko's transplanting that energy, then I'm inclined to think it doesn't actually have anything to do with the end of the universe, since removing heat from an already nearly-dead universe would be essentially harmless.
>Sono-G attempted suicide by hanging, hence the bandage around his neck,
This is ridiculous, Nasu would never write this. If you attempt to hang yourself you won't have a long-term scar on your neck, you'll just be dead. It also doesn't fit Sono-G's personality at all.
>This theory is supported by Grandpa Aozaki claiming that he had no interest in the dead
This could simply be a tie-in to the theme of Sono-G looking for purpose, as was touched on in his conversation with the priest, and it probably relates to some lore stuff we don't yet know from Mahoyo 2, and also it could be explained by my theory, since Grandpa Aozaki obviously wouldn't want to memory-wipe the cat now that Fate has reunited it with Aoko.
>and compared him to an insect.
This refers to the instinct and reaction-based mindless killing he was trained to execute as a SuperAssassin, Nasu went for similar vibes with Kiri Nanaya.
I think your theory sucks since suicidal people are inherently contemptible, Nasu wouldn't make one of his protagonists have suicide as a backstory.
Also all this stuff about being half-dead and therefore able to come back to life is total headcanon nonsense.
Also, if you want to continue spreading this dumb theory in the future, you should integrate my cat theory into it. Len's backstory is that she was a cat combined with a dead child, so you could say stuff like
>Sono-G is a male Len, he committed suicide and then Grandpa Aozaki turned him into a familiar using the cat's body, that's why he gets along so well with Alice (cuz she has so many familiars).