Maintenance for the week of April 20:
• NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
From what I have seen and know it works like this.
If a player vacates their Emperorship (by leaving the campaign while Emperor) and thier faction continue to hold the inner ring for 48 hours the next top player on their factions leaderboard will be crowned.
This also happens should the servers be restarted (often due to weekly maintenance) however I am not sure if this one is deemed an exploit, but as players have no control over stopping a server maintenance I personally wouldn't have said ZOS would rule it so.
So if there is no Emperor and no keeps have been lost the #1 player in the owning factions leaderboards will be crowned at the next downtime or after 48 hours.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."
48 hours, or something close to that. The faction that dropped emperor didn't lose an inner keep in that time period, so I'm not sure if that played a part in it. At that point it made the player next in line emperor.