Ultimate Weapon in Mideel

So I am about to go through that part of the game, and Ive been thinking... The mideel battle is already a part of the other world map encounters you fight with Ultimate Weapon... what I mean is, the HP you take off from him now, will never come back, so if you manage to do 10 K he will only have 90 K in upcoming battles etc... so heres the deal... What if say you get Barret to a 6-7 K angermax for 100+ K damage and kill Ultimate Weapon in 1 turn? Does he die? Does he flee and recover his hp full hp later in the game? IF he dies does he drop Clouds best weapon? Lots of questions as you see :p As anyone tried it?

If you manage to deplete all 100,000 HP in Mideel, UW will flee as normal. When you encounter it again later it will head straight for Cosmo Canyon where it will have 20,000 HP. Defeat it there to get Cloud's Ultima Weapon.