Re: OP
I believe my basic political fear is of personal helplessness and insecurity. Kafkaesque/totalitarian “order” and anarchy mark the ends of a spectrum from order to disorder; I fear both. From this flows the fear of both obdurancy and radicalism, because both invite instability to threaten the balance of order and disorder. I call the fear of obdurancy “progressivism” and the fear of radicalism “conservatism”. From a fear-based analysis, these are really the core of my political persuasion - every political position I take should lead back to these. By extension, the worst thing I have to fear in politics is personal helplessness and insecurity.
It is ironic that your hypothetical presumes the absence of conservatives in government. Actual exclusion of a group from positions of power is perilously close to personal helplessness - no matter how the exclusion was achieved. It does not necessarily imply personal helplessness (liberal governance may very well empower/uplift conservatives into bona fide liberals/liberal-conservatives), but in a discussion of fears rather than facts, you’re already within an inch of my heart. Neither is it necessarily implied that conservatives will face personal insecurity at the hands of a liberal government; liberalism as commonly understood would not tolerate any such treatment.
To answer the titular question with my own opinion, the worst thing conservatives have to fear is personal helplessness and insecurity. To answer your specific question, the worst thing all conservatives as a group would have to fear from exclusively liberal governance is… well, possibly nothing. I’m not sure if that’s the answer you were looking for. I’m using a very broad and idiosyncratic definition of conservatism; ask any non-liberal conservative about their individual fears in such a scenario and you will receive a more specific answer. I’m sort of a liberal conservative so, there isn’t necessarily anything to fear from a liberal government. I do worry about the possibility that proper procedures are overlooked.
I don’t think all conservatives have the same degree of fear when it comes to abandoning due process. By that I mean ensuring that laws are properly enacted and enforced. I personally rank it very strong, sometimes and with hesitation even above the normal concept of justice. The reasoning - in a fear based analysis - goes back to the balance of order and disorder. Without laws you have anarchy, insecurity, helplessness. On the other hand too much legalism leads to a soulless, heartless bureaucratic machine doling out injustices, shattering false security, and again, causing helplessness.
I don’t have any religious or ideological objection to same-sex marriage or legal abortions. I have some thoughts about taxes and healthcare but I don’t think my principles there are far right. I have strong legal objections to specific mechanisms by which those liberal goals are achieved. For example, I don’t believe the Bill of Rights is incorporated against the states by the due process clause (not that it should or shouldn’t be, just that it isn’t). I have a very restrictive view of the commerce power as written. I don’t believe a great deal of New Deal era legislation is constitutional (read: the regulatory state), let alone Great Society (civil rights, welfare) or some of the things proposed/in place today. I think the federal government has little to no authority to regulate abortion, healthcare, marriage, drugs, or guns whatsoever.
I don’t necessarily want social progress repealed - and I do consider much of that social progress - but I do think the courts could and should rule against progressive policies when the proper procedure is not followed. If you’re going to do it, do it right. Pass a better law, or even a constitutional amendment when one is called for. I think we need quite a few additions to the constitution - normal people should be able to point to the text that shows why the government can do X. This includes prohibitions on the states. Many foreign constitutions, even our state constitutions, are much more explicit in this regard. I think the people are more secure in their knowledge of the laws and the role of government as a result.
~Max