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.