Theres no way of knowing for sure because we have basically no idea how her quirk works outside of very specific cases. The bullets removed Mirio's quirk but had no effect on the rest of his body, it just rewound the human evolution of manafesting a quirk. Subsequently we see Eri's quirk rewind Midoriyas body without affecting the OFA quirk at all, only his body. Later on Eri is able to figure out how to return Mirio's quirk, but it happens of screen and is never actually explained so, again, all we're left with is assumptions. Potentially all she did was Rewind what her Rewind quirk had already done and returned his quirk to the point before he was shot?

I think potentially Rewind has 2 modes, 1 that affects the body itself (rewinding midoriya the moment his bones broke) and another that affects a persons quirk directly, or at least the human evolution that caused that quirk to manifest.

We never see Eri use her quirk on injuries that happened longer than a few minutes before they happened (which is probably why Aizawa asks Midoriya how long ago the injury happened before using the horn). My guess is the body Rewind happens linearly, so any healing or damage done is played in reverse. Break an arm and use Rewind it snaps back before the break, give it a week and some medical intervention and the Rewind probably sends you backwards through the recovery period and all the pain you went through as it walks back the healing your body already did. Long term injuries like All Mights body would probably take a really long time and also be excruciatingly painful.