Can windows server be upgraded from a mounted iso?

I have a windows 2012 server raw metal dedicated server hosted in a datacenter. (OVH)

It appears I can mount an ISO to be viewed as a CD with a drive letter, but if I mount a server 2016 or 2019 install media, if I start upgrading for that, do I risk the server rebooting during the upgrade, and then the media will not be available, so the upgrade is left in limbo between versions?

Or should I mount the image in the java KVM from my PC? Even when I have 1G fibre, the network traffic shows only up to 3Mbps, so it takes ages for the splash screen going to the first option screen.

Another option would be to copy the contents of the iso into a folder and run the install from there, if possible. Is it?

I've upgraded multiple windows servers that way, without a single problem. The iso is not needed anymore after the first reboot.