I do not know if X-Wing, Armada, or Imperial Assault (Skirmish Mode) have retirement schedules.
There is no published "retirement schedule" for X-wing. Some might say this is one of X-wing's problems as it goes into its 10th wave. As a player, I like the fact that they continually attempt to keep all ships (new and old) relevant. This creates a lot more work for play testers, but creates an ever expanding game that makes it fun to return to old ships.
I honestly would be shocked if FFG did not follow this same idea with Destiny. Make the cards/dice right the first time and there is no need to retire them.