But I found something interesting, when the mana void spawned and I was in Kitty form my mana did not drain. This means that potentially resto druids could shift to bear or cat and avoid the entire mana drain when they are healing, as opposed to say saving innervates for that part to have some mana.
I haven't yet tested this on normal/hc modes (will do that tonight!) but I would guess it to work the same, because that's how all mana drains in the games have worked thus far.
Anyway hoping some resto druids find this info useful!