Taking a year off without an injury as the reason should be unacceptable. Even with an injury, they should probably set a time-limit on how long you can wait between defending the title before it goes up to an interim title fight, then another length of time before the interim champ becomes the undisputed champ. It should just be written as a UFC rule.
For example: Don't defend for 8 months - goes to an interim title fight.
Don't fight the interim champ within 4 months after that, interim champ becomes undisputed champ. You want it back, you'll have to work your way back up to contention.