As far as I know, you don't really unsubscribe, just stop using it. If you want to stop getting e-mails, you can do that. The questions and answers stay forever, unless you delete them. You can delete the answers you gave, but not the questions you asked. If you want a question to go away, you have to ask the Yedda staff to delete it, or edit it into "---" or something.
If you are being presented with questions in your e-mail, and you want that to stop, you can do that. Deleting your topics of interest is one way. there might be an option you can select to not receive e-mails, but I never looked for it.
If all else fails, ask feedback, and the staff will answer.
