I just checked the Manual on page 7-10 and it doesn’t appear that the shocks and struts fall under the normal maintenance schedule other than to inspect and if necessary, adjust, correct, clean or replace as part of the suspension all the way up to 112,000 mi.
Normally shocks wear out and you notice a pronounced lean or sag. With the Nivomats, from some Chrysler minivan and Dodge Durango forums, people reported the fluid leaking at about 50,000 mi. But I really think it comes down to a number of factors like weather and usage before you have to replace them. But when the time comes the difference could be 5x more than standard and could cost as much or more than an air bag upgrade. Air bag systems date back to a 1957 Cadillac Eldorado so they’ve been around a while. I think Nivomats were first introduced on some BMW touring motorcycles in the 1970s and then the French tried them on Citroens followed by Volvo, GM, Chrysler, and others on family haulers as a substitute for air bag systems, so they have been around a little while. The basic difference is that the Nivomats are self contained and use movement of the vehicle create their own pressure/energy to raise the vehicle vs air bags and air lines where you add air and they self level by distributing pressurized air. But in order to be self contained systems, like the Nivomats are, they have more internal mechanisms that could fail. Chances are with harder use and worse extreme weather they are more likely to wear out or fail.
The Kia Telluride and Dodge Durango appear to be the only vehicles that advertise these Nivomats shocks as part of a towing feature and in my opinion that is a misrepresentation of the real convenience benefit. One disclaimer is that the Durango is sold as RWD or AWD so the rear suspension may work harder than the Telluride since the Telluride is a FWD based vehicle. If you plan to haul a lot that could push down on the rear axle they may help you and would be a nice benefit. But if you end up spending $900 to replace them sooner you might be just as well off with decent standard shocks and struts and an aftermarket air bag system that does have a more clear towing advantage.