I don't think PowerShell (and DSC) is that relevant in that kind of setup, scripting and automation tend to become relevant when you have a larger setup. It sounds like there wasn't much to automate anyhow (maybe system upgrades).
Also, doesn't at least Red Hat also offer a 10 year support cycle?
Personally I would raise one issue with Windows that seems to make UNIX(-likes) a better choice for this kind of setup:
System updates are problematic with Windows because of the need to reboot whereas of course on UNIX systems you only need them after kernel upgrades. I would wager that rebooting would be the thing that "breaks" an unmaintained box such as this one, some day. Then again, system updates are another candidate.