In 10 years I've used/installed a couple dozen AIO's . So far 2 pump failures one after 5 years of use and one in the first 2 weeks . Both corsair units. The 2 week old one was a silent death- no outward signs of failure, the other was a catastrophic failure popping the lid off the pump and draining a small amount of fluid onto the graphics card below as well as some onto the motherboard. I was in the room when it happened and yanked the cord out of the back of the PSU. I disassembled the system, cleaned it with QD electronic cleaner. allowed it to sit for a few days and everything came back to life.
The first one I bought is at least 10 years old, ( 120mm corsair) and it ran nearly continuously for the first 8 years or so then about 50% of the time since - still going though the cpu now has hotter temps at 4.7 ghz than it did at 5 ghz when new. No idea if its the pump, coolant , fan or paste.