After given it some more thought: yes, self healing pets would be no problem to mod at all, either give them a healing spell to use (that could be pretty annoying, but OTOH you could make it without sound or visual effects) or give them a regeneration ability.
A spell to heal your pets or followers I am not so sure. It could be that you cannot target your friendly monsters as normally all targetted spells are harmful and friendly monsters are usually protected from that. But hey, at least you can cast a Fire Storm and not worry about frying your doggie
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Rollo