Did you actually delete the message, or just archive it? If you were viewing the message and just hit the X, the message would have been archived and is retrievable. But, if you selected the message and went to "actions-->delete conversation" it's gone forever.
If you did just archive the message you can go to your inbox and click "other-->archived" and it'll show your archived messages. If you fully deleted the message though, Facebook doesn't offer any recovery support to get it back.
Thank you "calmstateofmind", for taking the time to reply to my quest.... I did delete these messages an d didn't archive them unfortunately. Appreciate your feedback much!
It's not possible if you delete All conversation so no one help u to back your delete massages ...... only on way u just contract Facebook customer supports to help you and guide you in better way....