As LimeLJ said, the transfer case oil pump on your NP231 transfer case only pumps when the rear output shaft is spinning. What you had going on was that the front driveshaft was turning the front output shaft, which turns the drive chain inside the TC (that does get immersed in fluid at the bottom of the case), and that turns the front drive gear on the output shaft, which isn't being lubricated. That's pretty bad. Damage, if any occurred, should be isolated to the one gear and the output shaft.
How far did it get towed?
At minimum I would do a transfer case flush and get some fresh fluid in there. Dig up the owner's manual, kindly let them know they messed up and that you're concerned about the health of your transfer case, and see if the they will cover it. Worst case scenario, you have to replace the output shaft (which comes as part of a SYE kit anyway
) and/or the front drive gear.