I think 110.12(C) applies here. I don't see any requirement for replacement. Drywall mud comes off of metal fairly easy, I think this panel could be easily cleaned up with a small nylon "toothbrush". After cleaning, I'd let your inspector prove that the busbars have been damaged by corrosion.

I'm sure in the future you'll be putting a cardboard cover over the panel when this drywall crew comes around. Seems to me these guys deserve a payback.

Tom

Few things are harder to put up with than the annoyance of a good example.