Maintenance for the week of December 1:
• PC/Mac: No maintenance – December 1
• NA megaservers for patch maintenance – December 3, 3:00AM EST (8:00 UTC) - 12:00PM EST (17:00 UTC)
• EU megaservers for patch maintenance – December 3, 8:00 UTC (3:00AM EST) - 17:00 UTC (12:00PM EST)
Campaigns end when their timer runs out - you can check this countdown in the Alliance War tab.
To leave a campaign you'll need to pay a fee, in Alliance points if I remember correctly - in order to leave.
You could alternatively assign yourself a Guest campaign, meaning you can play in that camp until your original one ends.
You will however have some restrictions in a guest campaign.