There's a really common notion among creationists that if dinosaurs were alive today, it would somehow disprove evolution.
I have never quite understood where this notion comes from, or what the rationale is behind it. I have never actually seen any creationist explain why this would be so.
The theory of evolution has nothing to do with when or how some specific clade went (or didn't go) extinct. Dinosaurs going extinct 65 million years ago has exactly zero relevance with respect to the theory of evolution. The theory does not deal with history and extinction events. It deals with the biology of large groups of living beings.
There have been actual cases of clades that were thought to have gone extinct tens of millions of years ago, yet only recently it was discovered that they did not. So what? It doesn't say anything at all about the theory of evolution.
I think this is yet another case of creationists having a completely mistaken notion of what "evolution" actually is, but in this particular case I am having hard time figuring out what exactly it is that they are thinking. I have yet to see any actual explanation from them on this.