I would have preferred if the chimera died, to bring forth character development for the MC, teaching him he cannot solve every problem perfectly.
but alas, this is not a manga aspiring to be more than a power fantasy after all...
Maybe it's for the narative.
It's known that the MC and the Lindwurm Guild have bad blood between them. If he goes back and goes, "Yeah, these ass holes have been doing horrific experiments on dragons" with no real evidence of such, then he's probably not going to be taken seriously because, even with hte MC's credibility, Lindwurm is still an S-ranked guild.
But if MC shows up with this never-before-seen breed of dragon? (I'm assuming that the chimera was properly fused into a single, whole dragon.) Well, that changes things, doesn't it?