I don't think I can outrun concrete that starts falling at the exact moment I start running. What I think is that the odds are low that the timing will be so perfect, and also that the odds of getting crushed under a desk are so much greater running would definitely have given my higher odds of survival in the specific situation I outlined.

If the face of the building falls off faster than they can get out to the middle of the parking lot then everyone inside is already dead too.