I assume damage from leaks isn't a thing with liquid cooled?
Is there much maintenance, eg topping off the liquid periodically, or flushing the circuit?
90% or more All in One Water Coolers are closed systems. Only some let you add more liquid but the amount you lose is very small over a few years... longer you use them, more you lose.
I am not in expert so won't try to explain how it gets out. Probably through the tubes that connect pump to radiator.
If my radiator leaked, the only thing under it is .... there is nothing besides the case there. It would depend which way the water went, could just go out from of case, or I would see it as it would be showing underneath the AIO rgb fans. there is a removable steel plate under my radiator - its there to hide the gap that is necessary if you have a 280mm or longer radiator in the front. Under plate is also nothing but if say case were tilted backwards, the water could eventually reach my PSU. But it take a while, and probably exit vents on bottom of case before then.
I am not going to think about if pump leaked as nvme & gpu are under that.
Leaks are possible but not common out of say the pump. It is a concern but not one I think about a lot. Besides not running PC when I am not here... not that I could do much I don't think. Would depend on amount I think.
they constructed in such a way to keep the liquid inside them and not let it out. Its not really water.
A friend with an ancient Alienware has been using same unit for over 13 years now. He is stubborn so I haven't argued about it.