Redditors after deleting their accounts with tons of karma:

I'm pretty you can still see them, but your username won't be shown. It'll display as "[deleted]"

Not as far as I know. But you could use something like PowerDeleteSuite to delete/edit all your comments before deleting your account. That's what I plan on doing. Just turn all my posts into Lemmy advertising, or just to tell Spez to go fuck himself. ;)

Edit, whoops, didn't see how old your post was. But hopefully it still helps!