Thanks for the replies, everyone. The date I was looking at was 9/17. And the flight is a 0645 departure, so it's the first flight of the day, so I assume the crew would be with the plane at least through to DEN?

There are plenty of UA non-stops around the same price, so that's probably the safest choice. I guess the bag fee is a small price to pay to not stop twice on the way to DEN.

Thanks again!