Elasa doesn't end until the battle is over, and none of the participants can retreat until then, thus the battle can't end with one side retreating.

So if someone pulls out a mutual KO, then this could end with no further deaths.

What would ME A++ even do? At A rank, it still only boosts all stats by one rank. Would A+ up the physical stats by a rank and a plus/two ranks, A++ all stats, and A+++ by all stats and requires manual control?