Just get the biggest honking Noctua fan+heatsink you can fit in your case and call it good. It's silent, simple, reliable, and if the fan does fail the heatsink will save your CPU.
Furthermore, you are supposed to use distilled water or non-water based coolants with high electric resistance.
https://www.leonroy.com/oldsite/img/IMG_1802%20(Large).JPG
Regarding distilled water, it is indeed not very conductive at all but it is also quite reactive and if it touches electrical traces and PCBs starts to leach ions from the surrounding until it starts to conduct at which point the machine will short circuit (speaking from first hand experience alas).
Seems like it would be easier to make a "never disassemble" system not leak.
Also not sure if you're counting AIO coolers in with water cooling but they are very reliable.
In my experience air cooling with a sufficiently large heatsink is simple and very reliable. Water cooling is more expensive, trickier and can fail catastrophically.
Source: Been rocking Corsair AIO coolers for around a decade now. I did have have the pump fail in one of them after around seven years of use.
On the other hand, a heatsink provides a decent amount of passive cooling all by itself, so when the fan fails there's a buffer that slows the rate of heating to a safe margin.
If one of the two fans fail i’d guess temps may raise a few degrees and that’s it. I could even manually test it with one fan and light loads to check one fan performance.
Perhaps if you don't forget to activate the BIOS CPU warning at high temp, you shouldn't worry about this .
I recently fixed a PC where the pump died without anyone noticed, and the only evidence, was that the BIOS was powering off the computer when the CPU gets too hot.
Bought the thiccest Noctua I could find on Amazon and haven't looked back.
I've got a custom loop with my Ryzen system (420 + 280 rads, mostly EK kit including a D5 Glass XRes) and it's been enjoyable putting it together, and if you're not totally incompetent easy enough to make leak-free with the latest generation of fittings.
As for a pump failing, as others have said the CPU will thermally throttle before damage is done, but for added peace of mind I'm running my setup with an Aquaero which will shut the computer down if the coolant temp breaches a set threshold, or it senses the pump has failed.
The biggest thing for me is that my computer is EERILY quiet unless I'm pegging all 8 cores, and the GPU, at 100% ... which makes for a nice peaceful environment.
Also modern CPUs have internal temperature sensors of course and don't 'burn up'.
This sounds like someone who is afraid of water cooling, not someone familiar with it.
The first rule of plumbing is that it's guaranteed to eventually leak.
(I don't know if this is actually a rule of plumbing, let alone the first one, but it sounds like it should be)
Also, FWIW: integrated liquid cooling solutions are if anything simpler and more reliable devices than fans: smaller motors running at lower RPM last longer.
Do I need to panic?