5th gear and there's no stopping me!
Join Date: Jun 2016
Location: NSW, Australia
Realistically this is a mechanic fix. You need the transfer case removed and repaired/replaced (I'm with landmannn - replacement is the better option and likely comparable cost to repair).
If it's an emergency you can keep driving by removing the front propshaft, although that's not as easy as it sounds on a Nav I don't think...
In the longer term if you're doing any remote area travel and want to add a layer of insurance, you can fit manual locking Warn hubs (would have to import from the USA as they were made for the Frontier). These allow you to manually disconnect the front wheels from the front drive apparatus, which has a tiny benefit for fuel consumption and mechanical wear, but is primarily useful for situations like this, and secondly useful so you can operate in low range gears in 2WD.