Hi leonsius,
Generally, Ryzen CPUs run quite hot and temperatures below 95°C are acceptable, however, the hotter your CPU runs, the less it will last in the long term.
I don't have an exact value in time, as it's different for each CPU, but if you were for example to run your CPU constantly close to 95°C it would surely last less than a well-cooled CPU.
If I were to guess, you could expect a well-cooled CPU to last 14-16 years, while a CPU constantly close to the limit would probably last 10-14 years.
Probably in 10 years' time you will already have another CPU, so unless you are hitting the thermal limit or you want to overclock your computer you can avoid an AIO.
If you see that this impacts your system performance (i.e. does not boost as high) you can go for a better cooling solution, but you need to evaluate well if it suits your needs (cooling performance/noise/good-looking factor).
An AIO is generally good, but it has some flaws, like:
- There is liquid inside, if there is any leak it will soak your computer, and after some time the liquid inside will become conductive, which could damage your computer in case of a leak.
- If you have an Air cooler you can always replace a fan for cheap, with an AIO, you have to replace everything.
- AIO tends to be more troublesome, if the internal pump stops, for example, it's quite difficult to notice. If you have a fan on a heatsink instead it's quite easy to see if this stops.
Before you decide to get an AIO, think about the points above. There are big (and sometimes ugly) heatsinks (i.e. Noctua) that perform almost, if not as good as AIOs.
If you decide to go for a heatsink, make sure to check for the clearance of your case. You don't want to buy a tall heatsink to then see that it doesn't fit your case 
