[Collector]

A good means of going about this would be to make KO'd targets enter a state where they can't be interacted with by living targets, and vice versa. In this way, Youkai wouldn't be able to take the FP from the summoner's FP pool to sustain themselves, and would be unsummoned during the next turn. This would also solve the problem of several skills and spells being applied to downed targets, rendering resurrection/death defying abilities less effective. A priest can Second Chance the basic attacker next to them for help, but they won't be doing much if they were just Adon Graxis'd while KO'd.

Make KO more impactful.

While Youkai contracts are definitely there to 'protect' the summoner, they have ample opportunity to do this before their summoner goes down. Having your summoner with 1000 base fp die while their six summons beat you to death shouldn't be a viable game plan, IC or otherwise.

Any sort of summon that lingers after their summoner/maintainer's death should be either removed from combat or destroyed.