I don't know about other people, but I usually don't bother healing peoples' pets. That's what Sustain is for; and worse case scenario, they can simply resummon them. No need to waste your mp on them. If the SMN dies, that pet is gone, too, anyway.

Also, unless you're party doesn't have a tank, I can't think of a reason the SMN's pet would be dying so often. Maybe your tank just couldn't hold aggro? o_O