Depends on the player. 'Open world' games, by definition, should always have something to do as long as you get to keep on playing after the credits roll. You can always roam around, collect cars, wreak havoc with the authorities, search for unique items/collectibles, complete that set of armor. Or even dabble in a different playstyle looking for conflicts.
Given all that, besides modding GTA games, I rarely play after finishing an open world game. Batman Arkham Knight was the last I played, and I made sure I did all I wanted to (everything besides Riddler trophies) before tackling the final mission because I knew I'd pretty much uninstall after that. However, the AR challanges give that game a lot of replayability (or should I say extended playability).