So who is the Understudy?

Barb, playing Mrs. Pendarves in Joyful Noise, went to the doctors: a tear in the retina. Now what? Julie, the stage manager grabs a costume and a script and heads out on stage.
Master Arts Theatre is a small community theater, we do as most community theaters, we pray nothing goes wrong with our actors. It has happened.
I remember during the production of The Last of Mrs. Lincoln, one of the actors was in an accident on the way to the show. What do you do? The director, who actually fit into the actors costumes, went out on stage with a script.
The Homecoming, Dale, who was playing dad, his wife was in a car accident. His son Greg was in the light booth. I went into the light booth between scenes and Mike took the script on stage.
Ask Tim what happens. Tim has stepped into two parts from the light booth. (Brave man)
What do you do? You just keep going. It is “community” theater after all.
P.S. Julie is doing a good job in Joyful Noise.