Strange thing happened the other day. A user phones and in a panic ask's "All our data is GONE on our list!" Stop the drama!
Anyway, here is the problem:
A Form Library lost all of its custom columns. Nobody deleted it. Opening the form in Infopath showed that the fields were still in the form. But the view did not show it. Not even in the library settings could you see the fields.
By luck, I think, I replicated the problem on our Application Support server.
Saving the List as a template, removed all the form columns in the list. The columns may have been removed from the view and list, but the DATA was still there.
So, here is the solution: Republish the form to the library. Open each item and view the properties. Then that will repopulate the fields .
If you experienced this, please leave a comment.