I've yet to come across a singer who minds doing their vocal again.

And I think in that scenario, if you have any kind of separation, separate the singer, even if it's to the point where they're not in anyone else's mic, if they're not spilling into anything else, you're pretty much good to go.

If they can be singing live and it's going into the monitors, assuming everyone's got cans, and it's a performance, and then they can redo their vocal afterwards, then you're kind of in a sweet spot.

Because in most setups... no other type of spill is going to be impossible to deal with, I wouldn't have thought.

I mean, I've done things on another session I did which had keys, two guitars, but an acoustic guitar as well.

So basically the keys and, like I think it was a Nord or something, an electric guitar and bass, I put all the amps in the corner, all literally right on top of each other.

and just mic them up individually as far away from the choir instruments as possible, including the singer.

You're augmenting the performance rather than augmenting the sound, but it's still making the recording better.