Most of the evolution we know about only occured BECAUSE of environmental pressure on existing species. So, assuming there are no environmental changes, the dinosaurs wouldn't change much at all really. Then again, mere separation (for example, two groups of the same species travel in different directions and live in new areas) can lead to small differences over several generations, until eventually they won't breed with each other (or if they do, it results in an infertile hybrid), thus the creation of new species. Oh, and fossil records show dinosaurs probably evolved into birds. Birds existed before the extinction of dinosaurs so it's safe to assume that with or without the mass extinction, all sorts of bird species would've developed.