When an account is deleted, posts made by that account _on the main site_ with a negative score are deleted along with it. (Posts with a score ≥ 0 are preserved.) Previously all negatively scored posts _on the meta site_ were also deleted, but [this behaviour changed very recently](https://meta.stackexchange.com/a/278218) and now all meta posts are preserved.  All comments are preserved, although like posts they are "anonymised" and attributed to a "user#####".

(For completeness, there is a stronger form of account deletion, called _destruction_, which will delete _all_ contributions by the account. This form is generally reserved for spammers and users trolling the site — so "contributions" is perhaps an overstatement — and additionally feeds into a system designed to prevent those users/people/bots from posting again.)