At the last match, a competitor was shooting an AR pistol with a red dot optic. Well, it died. He did not have irons also. So he gave up. I asked him, why not just try to shoot through with the little ol' window of the sight as an experiment. Just see how it works. He didn't want to as then he couldn't win or even place highly.
I would think that in the 'real' world, if that happened, you don't quit. Why not try it? Anybody ever try it just to see if you could get reasonable hits?
Yes, you should have backup sights. Wasn't my gun. I do on mine. Just a thought.