This FAQ When will inactive accounts be deleted? doesn't say anything about established user accounts.
An established user can:
permanently lose account access.
What happens to accounts of such established users?
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Simply put, Stack Exchange does not delete inactive accounts.
The answer in the question you linked outlines rules for deleting abandoned accounts, and for the purposes of that text, abandoned means an account that was created and basically never used. So if a user is fully registered and has more than 1 reputation, they're safe from automated deletions.
The death of users has been brought up before, but again, Stack Exchange is not interested in cleaning up or otherwise marking these accounts. So they will simply exist forever.
As an example, this user hasn't visited since November 27, 2008 and only has 3 reputation. Still not deleted, though.