Can it be done?

My original post was about the noise coming from my wifes 2004 expo and it turns out that it was not the wheel bearings but the gear box for the 4wheel drive. My question is how can it be bad? its just gears right? Seems like i would only have to replace a gear or so but she never uses it much in fla. So here is my question, can i safety disconnect it from the drive mechanism without any damage to the drive train and just not have 4 wheel drive? If so how and if not why?

Additonally how does the thing go bad in the first place. there is definetly some noise coming from it when i was doing about 60 but since i left the wife says she can hear it at even lower speeds and the shop that she goes to when im deployed or just underway said that theres something wrong with the shaft and it has about two more months before it goes out? I dont know what that means exactly by going out but my idea of just disconnecting it for 10 months or so seemed pretty good but i dont know about possible affects to other things.

I am in need of some really big help and i will be home soon to take a look at it so if anyone has any experience in this please let me know thanks.

I have read some about the vacuum hubs not fully engaging or disengaging and leading to problems in other areas, but I have no experience in repairing that yet. You might want to try these two forums:
Expedition
http://www.expeditionforum.com/f41/
F-150 which uses same system
http://www.f150forum.com/f4/