Nitpick: BTC can be worth effectively less than $0 if you buy some then the price drops. But in a Pascalian scenario, that’s a rounding error.
No, that would mean that you have an investment loss. Bitcoin is still worth $X each, whatever the new market price is. When you buy something and it goes down in value, its not worth less than $0, its just worth less than you paid for it.
I don’t think that the probability of Bitcoin’s success is so low as to qualify for Pascal’s Mugging status. While it is difficult to value the worth of a 5% or 1% chance of success, or whatever value one assigns, its still nothing like 1/3^^^3. It simply isn’t low enough probability, or high enough payoff to qualify as a Pascals Mugging.
If you want to actually approach Pascal’s Mugging territory with Bitcoin, then you need to change from the question “What is the chance that Bitcoin will capture 10% of the Gold market”, to something much less likely such as “What is the chance that (a future version of Bitcoin which uses its current blockchain ledger) will eventually become the main currency of a future post-singularity human civilization expanding outward at some fraction of the speed of light”.
When you imagine a scenario such as Nick Bostrom’s astronomical waste: http://www.nickbostrom.com/astronomical/waste.html and you ask the question “what is the probability that buying Bitcoin now would give me the resources needed in the future to allow us to colonize the Virgo Supercluster one second faster, thus saving the equivalent of 10^29 potential human lives”, THEN you can say that you are getting Pascal’s Mugged.
Or you could imagine other questions, such as “what is the probability that my buying Bitcoin now would enable me to secure life for humanity in a future run by an AI that is unfriendly but can be negotiated with, and has been programmed to desire Bitcoins?” Now you are actually being Pascal’s Mugged.
(Obviously these are incredibly low probability scenarios, not things that I think will occur. That is why I am using them as Pascal’s Mugging examples).