It would have been cool, but out of character. He had no reason to stick with you and every reason (based on his religion) to commit the honor-suicide. I don't know if Bioware would have given us another mage, either. Early in the game, if you're playing a non-mage, you have three mages, two warriors, and two rogues (unless you have the DLC with Sebastian). That's a fairly balanced party makeup, especially since you later lose Bethany, so you've got two of everything. Having a fourth available mage would be a little excessive.
If you're just going for the basic heal spell, I may be mistaken, but I think Merrill can learn it (though I almost never used Merrill because I dislike her character, so I'm not positive). Elfroot potions and the one that revives you right as you hit zero health are good for shoring up any holes in your healing. I found Anders only moderately useful as a healer. His main boon was that I didn't have to use a grenade to revive party members, but that was only usable once or twice per combat because of the cool down, so not incredibly useful on boss fights. Potions are your friend in this game.