If you click on a picture that Lightroom cannot find the folder that the picture is in, you get the message "The folder cannot be found"
You should be able to right click (windows) on that picture, and select find file automatically, using windows explorer search function.
After right clicking, you should then be put in Explorer's SEARCH DIALOG, which would automatically search for the file. (Right now, Lightroom will only go into explorer when searching for missing folders, but not the explorer with the search dialog. And that is only for searching for folders, not individual files, which lightroom doesn't even offer).
Then, when explorer finds the correct file, you left click on it, and then Lightroom would then reset it's file associations with the correct folder.
Pretty easy to implement, and would be very helpful.