That's predicted on if they do a show featuring her. Fans are basically saying there has to be a show featuring Chance when there actually doesn't. Your implication also seems to be that they wouldn't feature Chance if the actor isn't available when it's completely feasible. The real Chance doesn't have to be at the event at all. She doesn't even have to be in a show featuring her. They could do a Cirque style show with Chance on a screen narrating.
And the argument about a noticeable difference between performers only applies to those with a frame of reference, who are, again, the fans who see the shows multiple times. There can be a difference in energy in performances, but that can happen with the same actor every night.
I'll never get to see Lin-Manuel Miranda as Alexander Hamilton, a role he wrote and created. And he'll win a Tony for it. So I can complain that it's not him in the role when I finally see it, but I still won't have a frame of reference for the caliber of his performance. Someone who watches a HHN show once, similarly, doesn't know the difference. HHN is for THEM, predominantly. The fans who watch the shows multiple times are just cherry.