I had a t-case die and cause a complete loss of drive like that, but mine was a bit noisier. Happened on a trip to norcal (from San Diego) running up I-5 on the flat valley section pulling an empty 2H trailer (~3500#). First sign I had was the truck seeming to suddenly be in neutral and rolling while I was pulling out of a parking lot (acted as if I'd pushed the clutch in and was rolling for about 50', then caught again and was fine. Almost thought I'd imagined it as everything else was fine. Then about 50 miles later it suddenly dropped out of gear while cruising on the highway, then was able to jimmy the t-case shifter to get it back into gear, then repeated a few times and finally lost it completely. Thing is though when mine went IIRC there was a grinding noise from the t-case. Turned out that the pump has spun and the final failure was caused by wear on the shift fork allowing the shift collar enough slop to jump out of gear.
The fact that you don't hear any noise concerns me. Most thing I can think of would have caused some sort of noise either coasting or when you tried to move it. Only thing I can think of that almost certainly wouldn't make noise is a sheared trans output shaft aft of the output bearing. Possibly a clutch disk, sheared input shaft or t-case issue, but I'd expect at least some grinding noise from those.
I'd suggest pulling the 6 t-case flange bolts and pulling the case aft enough to see if the trans output shaft is turning. Should be able to do it without disconnecting anything else, just move it aft about 1/2". Might have to support it to keep the case from rotating. Then either jack up the axle and turn a rear wheel, pull the driveline and turn the rear yoke or put it in gear while idling and look at the shaft (easiest but most dangerous - be careful).
That should at least tell you if it's t-case or further forward. T-case is an easy r&r, likely not more than an hour and minimal tools. The case is light enough that a reasonably strong person case pull it without a jack too.
I'm not sure if you can see the trans in put shaft well enough through the inspection port to see anything - worth a look, but I wouldn't mess with it too much. Regardless, if it's not the t-case, the trans has to come out anyway, so not much gained pinning it down to the clutch at that point.