Main Quest Epilogue
Once Dagon is banished back to Oblivion, several things happen. Most importantly, all of the Oblivion Gates in Tamriel close permanently. Aside from Conjuration spells, the only Daedra left will be those in Kvatch. Secondly, all of the bodies from the fight to get Martin into the Temple will disappear from the streets. You'll still be able to see the marks where the Oblivion Gates opened in the streets, but the Temple district will be otherwise back to normal. The changes to the Temple itself (the broken roof and the Dragon statue) are permanent.
All of the random Oblivion Gates closed, but you might still find a couple of random Daedra at a gate that you found (got marked on your map), but didn't close before the final mission. Alchemists should periodically check those gates that you did find. Oblivion ingredients such as Bloodgrass, Harada Root and Spiddal Stick often spill through when the gate appears and remain after it is closed.
Any surviving NPCs (Jauffre, Baurus, etc.) will return to their original locations. But since the bodies disappeared, if they died, you can't even return their swords to Cloud Ruler. Cloud Ruler Temple is still open to you, though the Blades will have little to say that is new.
Ocato will return to the Elder Council Chamber in the Palace District.
Aside from the odd rumor, life will continue as it did before. Which just goes to show that the more things change, the more they remain the same.