About a year ago I got a leak upstairs that made a big stain in the dining room and I had to poke a hole in it to drain the water. Found the leak and stopped it, no leaks since. Now I'm thinking: What is the long-term damage that might come of this? Should I open the ceiling? I can feel no softness or creaking in any part of the ceiling below, and the drywall has gone back to dry. What if anything should I do?

Is this drywall? If so cut a square hole (16 x16) between the rafters and tell us what you see on the other side of the drywall piece