Q. Do I get to keep my title forever?
A. The Challenger, Rival, Duelist and Gladiator titles are redistributed at the end of each season based on your team’s performance. So for example, if you get a Gladiator title at the end of season 7, when season 8 ends you will get a new title based on your performance specifically for season 8. The only title that is permanent is the one awarded for the #1 ranked teams each season.

Source:
http://blue.mmo-champion.com/11/2241...wards-faq.html