Top West End shows have understudies of course for when lead actors are unavailable. When the Understudy is not available either, the "second cover" performs. This is rare, happening maybe in ten shows a year.
At one performance of Les Mis there was no lead, no understudy, and no second cover available for the biggest role in the show.
So surely they cancelled the show because no-one left in the cast was good enough to sing the part, right? Er, no.
A random from the ensemble cast stepped up, never having played the role before. and this is what happened...
Susan Boyle my arse. So many talented people out there already, doing real work for average or crap money.... Instead of being one of Simon Cowell's money puppets.
That is all.