Is it possible to restore deleted threads? I didn't know admins delete them. If I did I would have saved them; there were some interesting discussions. I really need them.
You can still read deleted posts if you have posted them and have a link to them (either via the 'Recently deleted questions' at the bottom of your profile – that link will soon show all your deleted questions).
Moderators do delete posts now and then, but for example this recent question of yours was deleted automatically because the system deemed it not worth keeping (it was closed and had a negative score).