I reckon their usernames might be recycled, and their tokens left alone, as a less onerous option. However, I don't like either idea, as if I got stabbed and needed to spend a few months in a coma, I'd be bummed out if Steemit gave my name away.
If there's a way to just remove dead followers, I reckon that would enable us to feel better about the accuracy of our metrics. Again, however, folks returning from comas might feel slighted by being bumped.
I note several noxious bots such as @a00 that are dead followers of mine, and don't mind bumping such as them. I don't mind ghosts so much, as I get all puffed up with self-importance when folks pay attention to me, even if they don't engage. (/sarc)