FMS a longtime user of CSE is now only a user #. There were some head butting issues with flimzy. Did FMS gather up his toys and go home or did the mods give him the heave ho?
Deletion of established1 user accounts is not something mods on this site ever want to or even can do. We simply don't have the ability to delete accounts, and kicking users out is not part of our duties.
Instead we have a way to temporarily suspend accounts that are being disruptive. This does not delete the account but temporarily takes away all posting privileges for a predefined length of time (usually starting with 7 days) and for a specific reason. The general category of reason would be visible on the user's profile for the duration of the suspension and the user will receive a detailed letter explaining why their conduct was disruptive and how to fix it when the suspension is over. If they repeatedly cause the same kind of trouble after returning to the site, repeat suspensions get increasingly long, up to 1 year. Mods cannot suspend for longer periods.
Such suspensions are relatively rare, and again they are semi-public. The fact that mods have taken this step is visible on the user's profile. The exact reasons and the detailed letter to the user are not public, but they are not private either. They are reviewed by both the other site moderators and CC'ed to Stack Exchange's community manager team.
Full deletion of a user's profile happens on user request only. This is done by emailing the SE staff or using the special form. They review the case and confirm that you really do want to delete. Two community managers have to sign off on the action and there is a waiting period during in case the user cools off and changes their mind. If nothing comes up to reverse the decision the profile well eventually be anonymised as you see in this case where their name is taken off all post content and the profile is removed.
This deletion process does not involve the site mods at all. In this example for instance I was unaware FMS had deleted his account until seeing this meta post. He's had periods of inactivity before and I had noticed I hadn't seen his name in a while, but I had not noticed he had deleted his account.
1 I say "established" because we can actually delete accounts below 200 rep, but this is reserved for dealing with spammers auto-generating accounts to post junk and generally not used for actual users.