So this was intended as an out of combat thing only?
It definitely killed me when I clicked it under 100% health which means if I click it in combat I need to lifetap a bunch of health back or rely on someone else to heal me. If I lifetap most of the lets say 8k back i'd need to spend about 1k mana. If someone was healing me they're healing a 2kish dot for 5 ticks on top of any other damage that might be incoming and that might be a problem.
Lifetapping - by the time the lich wears off i've spent half of the mana I got back just to stay alive.
Healing - If it's on a raid mob which is probably the most important time to use this I need to make sure 1. my healer is on the ball and ready to heal me over the next few ticks. 2. Hopefully there isn't any AE dmg inc at the time of the lich to make it worse.
I haven't raided with it yet just played around with it in town.
I guess I was imagining something like Canni V, maybe 20% hp for 20% mana over 5 ticks once every 9 mins.