the theory is that when the dollar goes down the tubes BTC will prevail, but I dont actually believe this. right now BTC is valued in $ terms, so if $ is worthless, so is BTC. There just isnt a complete BTC ecosystem. you would need to be able to do all transactions that are done with $ for BTC to be considered extant within its own ecosystem. that just does not exist. all BTC has achieved is to become a speculative instrument, its full potential has not been realized.
If it is just the $ which goes down, I don't think BTC will be worthless. It will still retain its current purchasing power, with some other currency (Let us say EUR) occupying the place held by dollar. You don't expect crude to become worthless just because the USD crashes. I expect Bitcoin to react just like any other commodity.
