Here is the deal with KDSS (from my perspective). It is a one off suspension wear part that uses hydraulics. Enough said.
It should last ~100K without any service, but beyond that is a big unknown. Suspension takes a beating, bushings wear, joints develop slop. The GX Lexus has had it as an option since ~2005, but I don't know the long term track record, just using common sense.
IMHO, it is a great option to get on a new truck that you plan to keep for a few years, not a great option get on a used truck with high miles.
If I had it and it went out, i would look for options to remove it, unless it was cheap to fix. Once those systems are opened up, the chances for future problems go up (again, just an opinion) It should be pretty easy to remove if you are willing to go without sway bars (long travel...). However, you might just be stuck with a light on the dash unless you can figure out how to disable it (I'm sure that gets very annoying). If you want to keep sway bars, it is an unknown, since the frame mounts are potentially different. I still can't believe Toyota would do a special frame for KDSS trucks.
Here is what I would consider attempting (never looked at KDSS setup in detail, but seems like it would be a possibility). Fabricate a fixed position cylinder mount to replace the ram (maybe even use the existing ram). Put a pin in it so that it can be manually removed. This would need to be well engineered and done by a skilled machine shop with some bushings.... Drive it on the road with the pin in, take it out for off-road. Maybe even put a few different positions in it for on-road. This is exactly what I wish Toyota (or some aftermarket company) would offer, a sway-bar system that can be manually disconnected at the trail.