Currently there is no way to cleanse the "Reduce Max HP" other than to die and revive. With the new W Chopper (I think it's Warrior)... the reduced HP cleanses when he dies, but that doesn't happen for any other characters.

There should be a talisman set or addition to some healer abilities to cleanse reduced HP.

Just an example: Asset's power ability could heal and cleanse reduced HP, while her fury heals and revives. Or Killer Ed's Fury could also cleanse reduced HP for allies. That sort of thing.