Usually you can tell whether the yeast in the dough was killed because the dough has no life to it. It will feel and spread just like putty or Play-Doh with no springback when you push against it. It will just go where you push it and sit there. I have made cold-fermented doughs that hardly rose at all but they were still OK. However, that is usually not the case where the dough has been at room temperature for several hours. If your kitchen was at normal temperature (i.e., not cold), the dough should have shown some signs of life.