Please be certain that your drywall is actually OK. This sounds like a bed for mold and future problems with that much water.
How do you know your insulation is not compromised?
If nothing else, cut a nice square hole and keep the piece and do some exploratory operations to see what is going on behind the wall.
If ok, then just replace that small square and mud it in.
Then there is a special primer that should go on the rock for prep for texturing, then one for after texturing before painting.
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