Ok so we know Overhaul lost his arms, and by extention, his quirk.
BUT.
He's still a scary dude regardless. If he were free, i doubt he'd participte in the war itself, but he WOULD probably try to continue his previous work. But the two things he needs to do that is Eri and his quirk. So that's it- he cant continue his work.
BUT HE COULD.
Remember, Eri is a child. A traumatized child. And despite what she has gone through, she was still raised by Overhaul (to an extent). Regardless, she's likely still very afraid of him (and anyone who reminds her of him which SIDETRACK IDEA: she's afraid of tokoyami bc his bird head reminds her of overhaul OK GETTING BACK ON TRACK NOW--)
So Eri is afraid of Overhaul. Technically there's no actual proof to confirm this, but lets be somewhat realistic here: theres no way she's not.
So what's my point here? And why am i narrating this like a really bad John Mulaney ripoff? I dont know, maybe its just me being mentally ill. BUT ALSO: My point is that Overhaul, if he were to find Eri, would no problem be able to scare her to the point of using her quirk on him, therefore restoring his arms AND BY EXTENTION, HIS QUIRK!!!!!!
Thank you for listening to my TedTalk
Now if you'll excuse me, i'm adding this to my list of "ideas i have that would make good comics or something but i have too much stuff to do to work on them".
Good day.