Unsure why plaster is damp, dodgy tiling, dodgy plumbing and dodgy everything but im still uncovering things a I only got keys two weeks ago.
Yes will replace the bath and everything else.
There isnt any plasterboard, just plaster onto brick infill walls, 50's ground floor council flat
Bit of a big job to take all the plaster back to the brick, would rather patch it in with something, can certainly take off the damp plaster or let it dry out. havent dealt with this issue before