water marks on ceiling from leak

hello, we've identified a leak in one of our pipes and unfortunately it has left water mark damage on the ceiling I was wondering if anyone could advise on this - does the ceiling now need to be checked and re-plastered and then painted - do this have to the entire ceiling or just the patched area where the mark is.
image attached - thank you!

Has the leak been fixed? if so wait 2-3 weeks for it to dry out. Then apply oil based under coat to the stain then re-paint the whole ceiling with with emulsion.

Andy