When an account is deleted, all data associated with that account is anonymised, the way that the account is deleted will depend on a variety of factors including how much network reputation you had when the account was deleted and how frequently you voted.
When your account is deleted, the following will happen
- All posts (questions, answers and comments) you've made will be anonymised and will simply display
user<youruserid> as the poster name
- All review queue history will be removed from the database
- If you were a frequent voter, these votes will be assigned to the community user, if not, they will all be reverted
- All of your edit activity will be anonymised and associated with the community user
While it is possible, in rare circumstances, to recover a deleted account, this is an extremely time consuming manual process that must be performed by Stack Exchange, and will only result in a partial undeletion. Undeleting an account is purely at Stack Exchange's discretion and is not a service they generally offer due to the time consuming nature. Account deletions are considered permanent with exceptions for edge cases.
In the event Stack Exchange were willing to undelete your account, you would only regain your post history (questions, answers, comments) and upvotes and downvotes associated with those posts. You would not get the following back, as it cannot be "undeleted":
- Any bounties you've earned
- Any reputation you've earned from suggested edits
- Edit history
- Review queue history
- Flag history
I will repeat, so you don't get your hopes up too much, but an account undeletion is purely at the discretion of Stack Exchange, and is a time consuming manual process. In most instances, it's quicker to just create a new account and resume your active participation in the site(s) you wish to participate in.