Even that scenario seems to suggest priors. Insane priors, but priors nonetheless.

You didn't get it straight. Having no priors means I'm allowed to answer that I don't know without attaching a number to it.

Conservation of energy is ridiculously well documented - it's not impossible that it will stop working on a particular date in near future, but it seems extremely unlikely (see - no number). The world in which it would be true would be highly different than my idea of what world is like. Other risks you mentioned don't seem to require as severe violations of what seems to be how world works.

I will not give you a number for any of them. P(earth just stoping|sanity) feels somewhat estimable, and perhaps if world is insane all planing is for naught anyway, so we might get away with using it.

By the way considering how many people here seem to think simulation argument isn't ridiculous, this should put very strong limit on any claims about P(sanity). For example if you think we're 10^-10 likely to be in a simulation, you cannot meaningfully talk about probabilities less than 10^-10 unless you think you have a good idea what kind of simulations are run, and such claim would be really baseless.