Ok…so '96 transfer case whines at speed

[cam.man67]

As mentioned in the other thread, I've got this '96 GMC 1500 with about 165000 miles. I've noticed humming/whining when the truck gets up above 50…it's actually louder than the motor at highway speeds, at least from inside the cab. Had a shop look at it today and the head mech. said the front (to the front axle I guess?) bearing in the t case was making noise. He's under the opinion that nothing needs to be done at this time, but quoted me $1800 to repair when it does truly fail. From the research I've done, it looks like I have a NP243.

My questions are threefold:
1. Is a noisy front bearing going to leave me stranded on the road?
2. Should I consider replacing or rebuilding the t case?
3. If yes, is swapping the t case something I can do? or, how hard is a t case to rebuild.

[EmeraldFlame]

a junkyard t-case is like 70$ here in self serve yards