Most likely, most of the data is still there. In order for the data to be gone, it has to be zeroed or written over. You'd have to inspect the drive some other way in order to see what has been written over.
Id be surprised if TM actually zeroed everything out. Must likely it started by setting up the format that's used by TM and started backing up data.
You might be able to view the drive contents with something from the Linux world, they probably have a tool of some kind.
Otherwise, you can have a pro look at it and see what's recoverable.
It's really an issue of how important the information on the drive is.
It's probably worth looking into software that reads formatted drives.
From a Google search: "Formatted drive recovery software"
http://www.yodot.com/hard-drive-recovery/to-recover-data-from-formatted-partition.html
http://www.wondershare.net/ad/data-recovery/?gclid=CPvCkpWvu7oCFURp7Aod8gwAYA
Note: I haven't used any of these before, but you might call their tech support and see if it can work for this.
Law enforcement uses these kinda tools all the time, so they are out there, just gotta find which one works.
