You're not wrong exactly, but I think you're perhaps assuming an unnecessarily absolutist approach. If there are legacy systems that need windows, keep windows for those legacy systems. What you're describing are exceptions, not the norm. The vast, vast majority of public service computers could just as easily be running Linux.

As for who the Federal government sues, that's why you go with an enterprise release like Red Had or Ubuntu. You find a company that you're happy to work with, you pay them maybe 25% of what you're paying MS right now, and in return you get a full support plan with clearly defined SLAs.

This isn't so much "Nothing's impossible" as it is "It's really not that hard." These are solved problems. Plenty of governments have already switched over to open source.

Just curious without knowing anything about the Canadian public IT system but are those ancient databases seriously running on Windows, or why would transitioning away from Windows impact their operations? As for transition, of course any transition is difficult and takes effort and careful preparation.

If Downtime is not an option, I am not sure how well the state is served by operating critical infrastructure on a system that the potential adversary has a prominent kill switch to it.

Regarding liability, well, I don't know how things are in Canada but the state doesn't sue if it is responsible itself and it can protect itself from liability if needed for cases where there is no grave neglect for example (or even for cases with grave neglect, that is a political question not for me to decide). Not saying that is necessarily a popular option but it is certainly an option.

PS: Isolated systems running on Windows are a non-issue for example. Other systems would need to be migrated according to a transition plan that can be more or less ambitious.