It depends on the platform and the campaign. There's no "winner" written into the game. That's the entire premise of the PvP engame, is the players fighting for control of Cyrodiil and the Ruby Throne. Sometimes the Emperor title changes hands several times per day.
ESO takes place in the 2E (Second Era?), and all of the others take place in the 3rd and 4th era. So anything that happens in the 2nd era is in flux(about 300 years), so they have a little leeway to make whatever happens canon.