You can always see your own deleted answers if you visit the page again (except in the few rare occasions of a hard delete). Deletions are by default soft deletions, meaning the content remains, but is invisible to all except
- the owner (in case of answers, deleted questions are visible only to the following groups)
- users with
>= 10k
rep - moderators
- developers
Those who can see the content can vote to undelete it. Votes to undelete self-deleted answers by the author are binding, as are moderators' and developers' votes. For ordinary high-rep users, it requires three undelete votes (in general), but moderator-deleted content can only be undeleted by moderators and developers.
Comments, on the other hand, are really gone when deleted, though not totally. Moderators (and developers) can still seesee them (but they are not shown to them by default, in contrast to deleted answers that are visible to them and 10k+ users automatically), but not even moderators can undelete themundelete them (developers presumably can).