I remember way back when (probably 1982) when James Earl Jones and Christopher Plummer did a run in Baltimore of "Othello." Christopher Plummer got sick and a bunch of people sought and received refunds. Then, James Earl Jones got sick, too, and they closed the show till at least one star was ready to come back.
Today, tickets usually disclaim the right to a refund if the star doesn't appear, or even if the PROGRAM changes. I've noticed that Broadway reduced tickets often coincide with a star's absence -- that's how I got to see some darned good substitute Phantoms.
I do think it's amusing that the tickets disclaim the right of the theatergoer for a refund when the SHOW changes. (Of course, this usually applies to regional venues and not Broadway). I'd love to see the result if a theater says, "I know that you didn't get to see The Phantom of the Opera on tour, but we had the right to substitute the much cheaper country singers 'Ozzie and the Ozones' and we'll honor Phantom tickets for that show."
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.