I don't think any of the NPCs will heal you even if they have the spell. Haven't ever had a mage follower though so can't say.
I've now given Derkeethus a chance for his arrows to burst on impact. Having exploding arrows has nothing to do with his personality, but it's really cool and I wanted another great archery follower, so whatever.
I've now given Kharjo the life detection effect I mentioned.
Illia has blood magic now, because that seemed like a freaking awesome idea and it kind of fits her anyway. You know what else? I like Illia. She's cool. I'm slapping the marriage faction on her just 'cause.