Up to you what you do and don't do. If you kill a summon you could just view that as purging evil forces. As I've said before: If you don't want to do it, DON'T.
There are ways around everything if you have the patience for it. Patience and creativity being key here.
I'm well aware that are truly difficult fights out there for casters that require serious forethought. My own caster is level 35 and seeing Elder Dragons now.
Healing spells work on your companions however. I keep Faendal healed quite nicely dual casting Healing Hands.
I was not going for a pacifist, I was going for a heavy armored knight with spells (spell + shield) with skills in blocking that would summon daedra and buff them with spells while healing them when they got hurt. That doesn't exactly work in Skyrim, I don't want to use companions either as that doesn't fit my character type.
With many of the early summons being easily brutalized by enemy NPC's and creatures I'm forced to protect my creatures by staggering and rooting them with spells like Paralyze and generally being offensive rather than focusing on just buffing or healing while being protected by my summons + large armor rating.
Would love to be able to summon my favorite Daedra, a clannfear and then throw a spell on it to increase its damage and a shield on it so it would take less damage while keeping heals at the ready for when it gets hurt. At least that was my vision when I first got the game.