Sorry, but if anyone here thinks that doing this show would not be harmful for Bart when he has a herniated disc, then you don't understand the condition. Walking can be a problem when you have a herniated disc and depending on how bad the disc herniation is, any physical activity like dancing, etc. can make the injury worse.
No one's health and future career is worth pumping up with cortisone to get through a performance. As I said in another thread on this topic, Lane had the same problem in the U.K. in the Producers and he tried to work through it and ended up in really bad shape. He is fortunate that he is doing OK now. This is nothing to mess around with. If Bart is in fact coming back tonight and he is OK, good for him, but anyone who has had a career on stage understands the pressure of carrying a show on your shoulders and you can easily talk yourself into trying to do a show when you are sick, based on the premise that the show must go on. I've done it and have been sick a lot longer than I would have if I had just taken a few more days off.
These are people we are talking about...not machines. If Bart can't make it for the critics, it is an unfortunate situation, but it would not be the first time. And Brooks should have considered a better known name for a "standby" than just to shove a kid in as understudy, though I heard Matthew is doing a respectable job.
The whole situation is unfortunate. I hope Bart is going to be OK.
"Life is a lesson in humility"