Could Eri Heal All Might?

ERI could heal Allmight's wounds for sure and it might happen, without affecting his memories. There is no reason why she couldn't do that, considering what she has done already.

Can Eri heal DEKU's arms?

no, the little girls power healed him during the raid.... It's possible it was due to the effect of his dream, though if you look closely when Deku is battling Overhaul with Eri's help his scars disappear after he defeats him.

Can Eri bring back the dead?

As far as I know, there has been no event yet in the manga where Eri was shown to have reverted a dead person back to life. What we know is that: Her quirk can only affect a person's physical state, as mentioned by Aizawa in Chapter 161.