This is debatable.
Issues are unavoidable, yes, but in hands of experienced users, they can be fixed and system will still work. My current Manjaro install on my main laptop is nearing to a 3 years. I use unstable repo since many months and I'm still well. This is how stable Manjaro can be.
There were many issues in that time and many times when I thought "aha, this may be the time I will finally will have to re-install the system" but it turned out there was a solution, always. In fact, fixes were usually very simple and trivial... so after a while they all go away from my memory as they were never there. I don't feel a burden of dealing with those problems, because it all feels simple and relatively quick.
So again, issues are inevitable, breakages... not necessary if you can restore backups, use tty or chroot. Rarely there are issues that cannot be helped through those methods. And actually, on my, I repeat, almost 3 years old install, I never had to use tty or chroot to fix any issues. For almost 3 years I did updates and system always booted successfully. Will it be forever so? Probably not but how long it will last depends probably on me and my tenacity to resolve things.
It is likely that the OS install will live as long as the laptop itself. If that happens, then this "Manjaro will break eventually" will turn out not to be true...