Sutton Ross said: "I know they just opened but understudies should be prepared from the absolute jump. This really sucks since this week is one of the most lucrative for Broadway but I'm sure they're doing the best they can. I get why people who paid a lot of money to travel to come here to see it would be very pissed tho."
There's several reasons why understudies and standbys aren't ready to go on during previews and right after a show opens. They rehearse during the day during the preview period. The show is frequently changing during previews. Lines changed, choreography tweaked, spacing adjusted. To have to go on without proper rehearsals or a put-in is incredibly nerve-wracking. Not to mention going on as the lead in a show without the necessary rehearsal time. Considering it's known that a good chunk of the cast and crew were sick last weekend lends to the likelihood of several people not being able to perform now. Having one person go on is one thing, but to potentially have several (5-6) understudies and swings going on without a rehearsal is insane to think it would operate smoothly.
A Chorus Line revival played its final Broadway performance on August 17, 2008. The tour played its final performance on August 21, 2011. A new non-equity tour started in October 2012 played its final performance on March 23, 2013. Another non-equity tour launched on January 20, 2018. The tour ended its US run in Kansas City and then toured throughout Japan August & September 2018.