All wheel drive not working

Nope. Without that front shaft there is not much you can do to be sure the case and front axle are okay. Did he say why the shaft was removed? Front axle problems? The Bravada is basically the same as a Blazer or Jimmy but with an optional automatic transfer case. You can have a 2/4/4lo case like the other trucks or the case with 2/4hi only that is fully automatic. The AWD case uses the ABS sensors and the vehicle speed sensors to determine how to split the torque rear to front.

No idea why the shaft was removed but thank you for the information. So the only way to truly see if it works is by buying a driveshaft, hitting the dirt, and trying to spin the tires right?

That or sticking it on a lift and seeing what works, that would be the better option if possible as it would at least let you hear it and see if there is something wrong before a part failed. I have done that out of the shop with a few using jacks and jack stands and removing the wheels. That lets you have someone inside and you can listen to each corner and axle. One common reason folks pulled them apart is to get better gas mileage, however you do not gain much by just removing the shaft. Now if you stick a two wheel drive transmission in there, removing the T-Case, front differential and the half shafts you might gain 1/2-1 mpg. Or if something came apart in the cases pulling the shaft would allow it to be driven.