Darn, you guys don't really see what summons are for don't you?

Equip auto-regen to all your characters and when you are dying, have Garnet/Eiko summon the summon with the LONGEST animation. You see those little green numbers popping at the background? Look at your characters' HPs.

Wow, they regened back to full health by the time the summon animation ended...so in this case, you have dealt damage and fully healed yourself AND give you some time to go to your kitchen and cook a bowl of noodles.