Momentum was shifting; if the game was five quarters long, they might have pulled it out! Alas... I'm pretty sure in the final analysis, Denver's defense shifted to "prevent" mode, and that accounts for why they were able to finally get yardage. It all seemed to be inside stuff, even when they were driving they were taking a fair amount of time to get down the field.
I didn't like the Vereen run for the failed two-point conversion; they were trying to spread the field, but there were still too many bodies in the middle to make that effective (and Vereen can't push the pile like Blount and Ridley). If they pull that off, the game might be a little different but they still didn't execute the onside kick.
Too little, too late.