we have realized recently at a customer's that worklow history is disappearing, which is, as we know (now :(), by design, but we need to get the lost workflow history back. We restored the necessary web app from a 2 months old backup, the history is present there, but we cannot find any way to copy it to the actual site. The documents and libraries are the same (remember, I use a backup of a current web app). We cannot simply use that backup, because it is 2 months old. We tried - in a test environment - also some database operations, but no luck. This wouldnt be acceptable in a production environment anyway. Any help would be very appreciated. Regards, Ravie.
What version of SharePoint are you using? If SharePoint 2010, you should be able to browse the content of database offline and able to export required items from there and then import it back to you live site.
If you want to disable the history clean up operation, you can do it. Visit this for more information: http://technet.microsoft.com/en-us/library/ee662522.aspx
Also, if you want to migrate items from one list to another, you can try using SharePoint Content Migration Wizard: http://spdeploymentwizard.codeplex.com/. I would suggest that you evaluate the configuration settings available while doing the export/import with this tool. The options are same as available with STSADM's -export -import operations.
We managed to create a feature that would show the WFL history, thanks to this: http://social.msdn.microsoft.com/forums/en-US/sharepointworkflow/thread/b15b27e2-3033-418b-9731-968273d7423e/