I don't think losing a Superbowl is the worse thing to happen to the Dallas Cowboys. Maybe if they had never won one I would change my thinking. If I were a Bills fan, I would point to that as the most disappointing thing. Dallas has won them before, so it takes the sting out of losing one.
I distinctly remember when they lost SB13. Sucked, but not the worse feeling because they won the year before. I thought the following season felt worse because Dallas had essentially the same team and could not even beat the Rams in the division round. The Cowboys should have been back in SB14 playing the Steelers, but instead got sent home by a not so great Rams team. That is more disappointing than about anything.
Getting to the Superbowl means the team did accomplish something. Not getting close like this year and in 1979 when they have a very good team is more disappointing in my opinion than losing the Superbowl. Even that is not as disappointing as going 5-11 for three straight years.
Losing is the worst and the biggest disappointment of them all. Even when expectations are not that great, it still sucks to see the team you root for having losing seasons. I will take this year over any of those seasons when the team had no direction. Sure I would take a Superbowl winning team over anything else, but this year is much better than some of the worse alternatives I have seen Dallas go through.
If anybody would rather go through three straight 5-11 seasons over losing a Superbowl then you need to go see a therapist. But wait your turn, I am still in my session.