I guess your right. Is a revenge ending possible?
It is mentioned, yes. Will it happen, we really not 100% sure.
Also, there is also the plot of BBP to consider: Let's imagine what would happen without Kurt.
Arika and Terena are descendants of the legendary hero, so they would have to go, in order to defeat the demon lord. Unavoidable.
Rietta became childhood friends with the girls after leaving the capital, but would she still follow them to the capital without Kurt being with them? She could also stay behind, as she doesn't want to go back to the capital, but Amor would stil be after her from behind the scenes, if he is not stopped that is.
The girls would likely be corrupted much earlier against the plant monster early in the game, without Kurt being there to save Arika while Terena is busy dealing with the other one. That would just rush the plot and cut the game shorter.
Terena teaching Kativ was part of the deal to let the girls live in the lord's manor for free, so the molestering and sex with Kativ would likely be unavoidible too.
The trap in the library would still be likely to happened, if the Plant Monster incident was avoid from worst case scenario.
Arika would still "entertain" the lord until she finds the book, that can temporary nullifie the aphrodisiac toxin, free them all.
Here is where it could get tricky; without Kurt to be charged for the crimes he didn't commit, the men would think of a another approach to "reclaim" them.
But that may still involve going into the "goblin hideout" where Rietta and Terena were captured, but without Kurt, Arika would likely be caught too.
The girls may be charged for the "crimes" (not necessarily the same crimes) like Kurt, and here comes a few issues:
Rietta may happened to be brainwashed regardless of the circumstances leading up to it, so there is little problem there.
Terena only used magic on Kativ, because he falsely accused Kurt for kidnapping him. Without Kurt, there is little reason to use magic on him. Unless there is a new reason for her to use magic on him.
Arika is the biggest problem of the 3.
Arika only made a deal with the Lord to protect Kurt. No need if Kurt wasn't in the story.
Arika would be wearing the clit-ring, that would make her horny but also lose her feelings for the one she love everytime she cums with her clit. Wouldn't matter if she didn't have a lover to begin with.
The lord would then go for a different aproach, to capture Arika's heart (and body).
Conclusion: The two other girls' story may not change much, but Arika is closes to Kurt, so her story would have to change to a certain degree. She could have gone a different transformation even.