Have not completed the game yet. Just taking my time and enjoying it.
The question I have is the missions in game, once you complete the game are you able to go back and replay them with friends? Just like you are able to do in The Division and Destiny?
You can replay them both solo and co-op. Go to the map and you will find on the left beneath the buchons picture the key-binding to open the mission selection for the region. Or go to the cartel overview and select the person.
Side missions can only be replayed in co-op, not single player though.