I have drilled through 2 water pipes - (not just 1, bloody typical!) ant the contents of the cistern and header tank have gradually drained through the ceiling into the lounge.......but with opening the taps, catching 70% of the water by stabbing holes in the plaster board and catching it in the recycling bins(...pretty quick thinking) and the other 20% seems to have been absorbed in the rug, the only damage seems to be a bit of staining on the ceiling and the 3 stabs i made to drain the water...the wood floor was dry inder the rug! I'm thinking good day...just need a plumber to fix the pipes now!
I had a similar leak a while back. Now I have cracks where the plaster board joins are. Also the skim coat popped out lots of little holes where the heads of the screws are. This was with the water proofed stuff as well.
If you drained it quick the plasterboard will be fine. Let it fully dry out before filling the holes and re-painting. Really shouldnt be a problem.