Sorry. I type quickly.

Mikhail has a penchant for surviving when we don't expect him to possibly do so. Some theories that are floating around suggest that dead people on the island can reawaken in some form or another (i.e. "undead") as long as they are not buried (if they are buried, they have only shown up in other characters' flashbacks, hallucinations or dreams). So perhaps, Mikhail is actually dead but still animated.

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Abaddon