Hi - if you are using the integrated version, here is some important info:
If the whole document is deleted in Workfront, the proof (and its previous versions) are restored as well when you go to the recycle bin in Workfront's Setup.
If only a version of the document is deleted in Workfront, you cannot restore it in Workfront.
For that lost version... you can go into the ProofHQ side and restore that one version. You can then go back into Workfront and in the Add New drop down for documents there is an option for From Workfront Proof. The version is separate from the rest of the versions, but at least it is not lost. In our trainings, we BEG project managers not to delete versions of documents and proofs because of this. (Also, the number is off as WF will continue the numbering but Proof renumbers everything). Hope this helps. Anthony Imgrund FCB