Ceiling stain

[Bienes Raices]

There was a leak at some point, either from the plumbing or Hurricane Charley (I know the roof was replaced in 2004). Would you just leave this alone, or would you have to have someone replace that part of the ceiling? (The roof itself looks like it's in very good shape from the outside of the house). I'm not sure how big of a problem/expense something like this is.