What happens to opponents that get defeated in battle. Do they disappear or simply weaken?
I think they weaken because:
1. I would be cruel if the Spiral Cup competitors that lost disappeared.
2. Cyrus Drake becomes your guide through DragonSpyre after you defeat him.
3. Khai Amahte the Great is in good enough condition to rejoin the order of the fang after you defeat him.
I think they disappear because:
1. The narrator states after many boss battles that they disappear.
2. Krokhotep turns into a ghost who guides you through the Tomb of Storms after you defeat him.
So which one is it? Do they disappear, or weaken, or somehow both?
It depends. Cyrus surely doesn't weaken or disappear. Defeat is just that...we don't "kill" anyone so they don't disappear from life, they just go about their business.
For starters, if you're talking about street opponents, (not street bosses) they just disappear for a few seconds and then reappear in a different place. If that didn't happen, then there would be a shortage of monsters to defeat, and that would definitely cause problems (especially if you had to collect a lot of things.)
If you're talking about bosses, well the quests ones (if defeated) are just like us really. You defeat them, they talk to you (or thank you for freeing them or something) and then they reappear back in the tower (or occasionally the street) and you can defeat them numerous times over and over. If they didn't have that then the term "farming" wouldn't exist.
i judge it off of how they die. Like the rotting fodder goes into the ground and dies maybe, while Cyrus Drake or Chester Droors just says hey you weakened me good job blah blah blah.