only one bad thing happened, at least from my perspective.
Of course during all the craziness I didn't go over with Father (we don't have a deacon) his, "This is the wood of the cross..." I didn't even think of it as being something I should have made sure he had down, but when he sang it, he went back down to the opening pitch on the word "on," instead of staying on the same note he had just sung for "cross," so he ended it way lower than it was supposed to be. So here I am, up in the choir loft, and now we're in some weird mode, so I had to decide if I should start the choir on the same note he had ended on (which was the wrong note, but everyone knows they're at least supposed to start on the same note as the priest ended!) or should I jump back up to the right pitch and put us back in the right mode/key. I did decide to just stay on the same note, and the people's response ended pretty weird and was also in a confused mode, and this happened all three times.
I afterwards explained to Father what he had sung wrong, and he was surprised, "I practiced it!" So I added going over it before the service to my list of things to do differently next year, (also including things like: have twice as many songs prepared for the veneration of the cross-yikes! And even though it's not necessarily called for and we are already doing a lot of singing, it wouldn't hurt to have another song while the collection is being taken up and the altar is prepared.)
But the choir DID successfully sing everything a cappella, which added a loverly simplicity-reverent atmosphere! And my cantor nicely got through the psalm, which was the only thing I was actually worried about doing unaccompanied.