What would happen if I ignored my noisy rear differential? Some people say they can go for a long time like 10 yrs?

Worst case the internals of diff explode making your car impossible to drive requiring at least a new rear diff at the most a new rear suspension setup that would cost more than your Durango is worth in effect totaling your SUV.

A very possible worst case: The bearing(s) heat up so much as to ignite the rear end fluid, and it catches fire. Debris in the bearings have caused the rollers & races to become pitted, hence the noise you have been hearing for some time now. The debris along with the pitting creates much more heat than the fluid was designed to tolerate and it could ignite. The high heat will also cause what's left of the pinion & axle seals to melt & or catch fire too.

Make sure the lube is clean and up to the correct level, They type of noise is worth noting they can be a bit noisy for years also as long as it doesn't get worse.

I would go and get service.. change diff fluid and new gasket.. should be around 100 bucks.. 90 percent of the time it fixes noisy rear ends..and it would avoid costly repairs..

Just don't drive it more than 25 miles an hour or on public roads.

When it fails, you don't want to die or kill someone else because you are too cheap to change the fluid.