I feared he would be martyred, when he returned to Russia after getting poisoned by the FSB and helping Bellingcat track down the agents who poisoned him (nobody in power did anything about them). Back then, his life was saved by a pilot deciding to make an emergency landing and a doctor suspecting a neurotoxin.
What finally took his life will be difficult to ascertain due to lack of transparency - a remote location, an extremely authoritarian system, war, politically controlled law enforcement and courts. Still, a day before death, Navalny appeared in court for another potential addition to his already 19-year sentence - in good spirits.
During Navalny’s imprisonment, the regime made a sustained effort to break that spirit, issuing a constant stream of disciplinary punishments (a total of 27 times): for not placing his hands behind his back, for incorrectly introducing himself, for uttering a profanity, for failing to clear leaves in the yard, for citing the European Court of Human Rights’ demand for his release, for addressing the guard without using a patronym, and for declining to wash the fence.
They also transfered him to the far north and previously used sleep deprivement against him. I tend to assume that they also killed him, either directly or indirectly.
He was definitely not the perfect politician, but did things which a common politician never dares to do, which suggests having some principles. When they came for anarchists, he didn’t forget them, but also spoke for anarchists.