ISuMin

Since all of it happened in a day then if everyone who knew about him being branded today will die including the rest of the main clan, then he can walk in Konoha without a seal as if nothing happened, under the sad fate of the last survivor of the main clan 😢.

People from MHA don't have cursed energy in them nor are they mages or shamans nor are they all stronger or faster than ordinary people if they don't have a corresponding quirk for it. Stop pretending you don't understand what I'm trying to convey. There's absolutely nothing that will shied Shigaraki from the fate of his sidekick except your illogical opinion of him being STRONG just because he is able to kill someone on touch through decay. How is he different?

First hokage cells

Let me phrase it differently) You shot someone in the head with the glock 19. How being more buff or lifting more in the gym than his neighbour, that was also shot, will help that person survive? There's no difference.

If someone can't reassemble themselves after being blown up then

It's subjective. Like in Naruto, even if someone can erase a mountain they can still die from being stabbed by a kunai. So, I don't know who came up with an idea like that but it's stupid to apply it anywhere else except of xianxia, where the cultivators are made of energy.

Should have used it on Shigaraki

The timeline is messed up. First you had wrote that Orochimaru lost his hands and now this.