No Immortal Inertia: Averted. Biology does not work that way. If you stop taking – or somehow take away – the immortagens that made your cells all youthful, well, your cells are still youthful. You’ve got a full natural lifespan to go find some more.
Longevity Treatment / Immortality Inducer: Immortagens, which are Exactly What It Says On The Tin, along with mind-state backups. (Previously anagathics, too, but technology marches on, etc., and why settle for a few extra centuries when you can aim for eternity?)
The Empire, or groups within it rather, works hard on selling these to absolutely everyone, on the entirely reasonable grounds that anyone who wants to die and/or doesn’t want to not die is obviously nuts, and anyone who advocates for death in general is even crazier than that. (See also: Immortality Immorality.)