Dinosaurs were doing fine right up to the impact; there is no good reason to think they were already in terminal decline.

But yeah, there's been a back and forth about whether dinosaurs were already on their way out or were they a bit limited by the very end of the Cretaceous. I think the more recent analyses have shown that's probably not the case, because in other words, they were basically doing fine right up to the extinction event. And so yeah, if the asteroid hadn't hit, there's no reason to think that they were on some kind of terminal decline.