We had the second female lead (Irene Malloy) drop dead of a drug overdose during a private school production of Hello Dolly! back in 1973 or '74. This was in a no-expense spared production, with all of the trimmings, and she keeled over in the midst of the "Waiter's Gallop" at the dress, putting a real damper on Act Two. (We got to go home early, but still got paid for a full night's work.)
(I knew about the overdose as my cousin's wife did the nursing on her comatose body when she was hauled to the hospital. Nothing was said at the school, nothing at all.)
The school reached out to a local college program and paid through the nose for a replacement, who came in and aced the whole production. The most eerie thing about the whole episode was that not a word was mentioned about the dead girl, even though the programs had her prominently listed, with a huge cast bio in the bargain. No dedication or anything; those Catholic schools weren't about to point out that one of their clean cut young ladies was anything but.
Well, there was that and the guy with the 1890's, barbershop quartet haircut (complete with moustache and hair parted down the middle) who played both tuba and string bass. I never saw him again, but damn, that guy was good.
