If that system was mission critical, would you just leave it running there and not pay attention to it? No monitoring whether the VM is running, the disks are f

If that system was mission critical, would you just leave it running there and not pay attention to it? No monitoring whether the VM is running, the disks are full, the processes are down? Paying attention doesn't mean that you have to personally look at it every day. Set something up to let you know when something isn't right. And as you mention: planes get maintained. Nobody lets a plane fly for 20 years without paying attention.