Are the files deleted from the phone or the computer? I screwed up and deleted my entire iTunes folder a few weeks back off my Windows 7 computer. Talk about stomach in the mouth experience!
Anyway, I wondered if I could do a system restore. That failed. Said could not hook up or find Drive C: So, I said BS, if C were not there, the computer would not work.
I opened up My Computer and brought up C Properties. There is a tab there Previous Versions. I opened up one of the older Previous versions and there was all my music. I just drug the iTunes folder to another explorer window and BOOM I had my stuff back.
So at least on the computer, anything you delete is still there in your Restore point previous versions, or whatever that is called technically and you can retrieve the entire disk if you need to or just certain files or folders you want back.