Healing magic isn't exclusive to the religious at all; it's just a particular branch of things to learn. Its closest related [i]other[/i] branch is necromancy (which is amusingly similar to I think AD&D), particularly the more benign side of things.

As for schools, do you mean as in "here is where you would learn magic" or breaking it down into e.g. evocation/abjuration etc? In the latter case it's more a matter of most mages (and certainly most mages both young enough and willing to adventure or fight and [i]not[/i] be reclusive academics) predominantly mastering one area, much like how most warriors do not master every weapon and martial art that they come across.

Working on a map of Estival specifically now.