Try emailing supportintl@dtp-entertainment.com or support@larian.com.
This problem had been reported in the forum, as well as a couple cases where he is unresponsive, but pretty much just in the topic
Where is Captain Rodney?.
There have been a couple cases of NPCs missing in specific locations, which leaving and returning resolved. I don't know if the same thing would help for a specific NPC, though. You could keep playing and check back for him later, or (if you've cleared that far) take the path in the far south west of Broken Valley to enter the Orobas Fjords (the start is safe, but heading down the mountain path you would soon start running into level 18 opponents) and then return.
