fix the easiest first for transportation.
you can drive your pickup without activating the transfer case, and drive it just as rear wheel drive. Does that work?
usually u joints give you some kind of hint they are getting ready to let go...like a ticking sound, or a muffled bang when putting it in gear...due to the play in the driveshaft. But, yes, ujoints do go bad. i like to buy the kind with grease fittings and each time i am under the truck for whatever reason, i shoot some grease to them. Sometimes the grease fitting is hard to reach with a grease gun and the shaft has to be removed to grease em up.
if your front slip yoke came out, which i am sure it did, ensure your trans fluid level (since you say you can't get the tires to spin) is correct. fluid will drain out the tail of the trans.
when it rains it pours....or i should say, when it snows, murphy's law takes over. anything that can go bad usually does. we saw rain in Richmond yesterday, the first time i have seen rain in two months!! it has all been snow before yesterday.
**another thing, you say your truck won't go anywhere now, even though the driveshaft is in place? Make sure your rear end U bolts holding the rear axle to the leafs are fine. If your driveshaft wont turn the rear end now, even though you put it back, the distance between the rear axle and trans may have increased, thus, causing the front slip yoke to slip out of the tail of the trans enough to where the splines don't mesh. This is a long shot, but worth checking nevertheless.