i recon also to make it interesting you should have it so that the reviving hero starts revival with hp of 1 and the user can not control him (mabey pause hero) then, very quickly regenerates health, however if he is attacked while he is regenerating then the regeneration ceaces and the user is granted control of the unit again )regenerates mana so that the mana and health should both finish regenerating at the same moment providing it is not interrupted.
Yeah.. That will make one hell of a revival system.