I guess we could probably do it theoretically, yeah! The danger really lies in that none of us are trained medical professionals, obviously, so we don't know anything about the human brain-- and all of the dangers associated with that. Even if the tools are magic, magic only gets you so far if you're poking around in someone's brain and have no idea where to cut. So far I haven't ever come across a wound that the magic gel couldn't heal, but the real worry is if the patient dies before we're finished...
We can restart the heart if it stops for an instant, but... once they're proper-dead, there's nothing we can do about it.