That but allow the history/comments?

If you no longer wish to access your account set up a new autogenerated password then forget it.

Usernames themselves can be linked and associated around the web, and they chain all the posted comments to a single identity. Changing to [deleted] at the very least provides better protection.

A bit more stronger than that. Have a [deleted] user tag. Deleting all comments too would be nice but I get that it messes up the comment system.