Actually Scientifically, unless scientists could look over ever inch of the earth at the same time and see that no dinos exist, only then could we say that they are "extinct" but it is because of evolutionary ideas that we are lead to believe that they don't exist.
I'm afraid at that extreme (every inch ... at the same time) your suggestion is obviously very silly. Let's say I could scan all of north america at once then 1 month later all of africa and found no dinosaurs. Then at monthly intervals the rest of the continents. Could I then not safely give a high probability conclusion that there are not dinosaurs? If not why not?
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