The Nissan Path

I will start with my question and follow with the details:

1. Do I pay $2000 to put a new transmission in my 1992 Pathfinder?
2. If I do, is it still reliable (as in, can I go on long trips and over mountains)? Lowest mileage transmission the garages have found are +170k miles
3. Is the transmission the real problem, or a symptom (read some stuff about coolant leaks into transmissions)?

Car:
For reference, it is a 1992 Pathfinder SE with 105k miles on it. I recently replaced all the belts and oil and got new shocks about 2 years ago.

Story:
I was driving over Snoqualmie Pass in Washington over Memorial day and my A/T Oil Temp light came on. It took me ~15 min to pull over, but I slowed the car and kept it under 3k RPM (and didn't feel or hear anything off). I stopped for 5 minutes and then crossed the street to park the car for longer and screeetch...now my transmission is shot and I'm looking at $2,000 to replace (would include radiator replacement as well)

The engine coolant ruining transmissions applies to the 2005-10 models. The radiators are often replaced with transmissions on earlier models because of the finned cooler used inside the radiator for the trans fluid. They tend to trap debris/clutch material when the transmission fails and they can't always be flushed out.
I wouldn't trust a used transmission with well over 100,000 miles on it and that'll be hard to find considering how old these vehicles are. A rebuilt or reman transmission might make sense if the rest of the vehicle is in good, mechanical shape and there are no corrosion issues with the body and frame. Only you can decide whether the vehicle is "worth" your investment, or better off being sold or traded-in on another vehicle.