Pages tagged with DeletedPage are deleted after two weeks (actually, the expiry timeout of the KeptPages) of no edit activity. In practice, this usually means after someone important remembers to do maintenance.
Pages that are deleted are permanently lost. They are not restorable from any backups you may have heard exist, not matter how reputable the source of that rumour was. Backups during live script development have been safely lost. Therefore, it is up to the community to ensure that pages aren't deleted recklessly.