I've not seen that before!
Rear Counter-shaft nut appears to have come loose, and that almost looks like the rear CS bearing poking through
It would have just walked 5th CS gear off the back of the shaft, the nut has dropped down into the bottom of the housing.
So my guess would be to replace the extension housing, bearing and nut.
Make sure the rear CS nut has Loctite applied to it during reassembly...
Take pictures of the disassembly!