Many years ago, I saw Dudley Moore performing his score from Bedazzled at the piano with a full orchestra. He had a memory lapse in the middle of it and had to stop the orchestra. Moore just laughed it off and said, “That happens sometimes! We’ll start over!”
At the time, I didn’t think this was a big deal, and I don’t think anyone else at the concert did either. Yes, it’s perfectly possible for a performer to screw up music that he actually wrote, and Moore handled it professionally and with good humor. Years later I realized that this was probably an early sign of the illness that eventually killed him.