something like 'simulationist' preservation seems to me to be well within two orders of magnitude of the probability of cryonics - both rely on society finding your information and deciding to do something with it

I don't know if I agree with your estimate of the relative probabilities, but I admit that I exaggerated slightly to make my point. I agree that this strategy at least worth thinking about, especially if you think it is at all plausible that we are in a simulation. Something along these lines is the only one of the listed strategies that I thought had any merit.

A priori it seems hugely unlikely that with all of our ingenuity we can only come up with two plausible strategies for living forever (religion and cryonics)

I agree, and I also think we should try to think up other strategies. Here are some that people have already come up with besides cryonics and religion:

• Figure out how to cure aging before you die.

• Figure out how to upload brains before you die.

• Create a powerful AI and delegate the problem to it (complementary to cryonics if the AI will only be created after you die).