I offer permanent bans. I've dealt with too much of the "Woe is me" bs and then they want their account back 2 weeks later.
Simply put I tell the users once they've contributed, they've contributed and if I delete them it does not remove what they have done. A permanent ban is more sensible. Besides it's good for you to keep track of 2nd accounts unless you're into making annoying little notes about annoying little users.
Due to the nature of Internet spiders and search engine indexing, information and content, once posted on the Internet, usually becomes permanent, so please remember this when hitting the 'submit' button. As a policy we do not prune user accounts, unless they have zero posts. We believe a user has actively decided to participate in a community, and understands that submitted content such as a profile, or a post, can be retained at our discretion (usage rights). Removal of accounts with post content would leave the conversations within threads incoherent and difficult to follow. In other words, once it's here, it's here, so be careful what you post.
I wont delete or ban in response to a "quit" request. I just tell them, "okay, go...and come back some day if you feel up to it".
I will not comply with the "I'm taking my contributions with me" meltdowns.
I wont delete spammers either. I ban them. If you delete them, them bots just sign up for another account. At least if the account exists, although banned, you can refer back for data collection purposes. I find the IP data to be helpful when blocking IP ranges.
I seldom get spam any more since I have countries like China, Russia, India, Nigeria all blocked, since that is the bulk of the spammers. I know this method might not work for sites that target the world, but my site is a community site whose demographics consist of pretty much just the US.
Don't do anything with them. 90% of the folks that suffer meltdowns will reappear at some point...that is, if their account still exists. Banning their account just makes it permanent....then they wont return.
If the person insist that you delete their account, ask them to take a 30 day break from the board...then message you after thirty days requesting the account be deactivated. These requests are usually heat of the moment requests. I would not take any action that seals their resignation.