BitCoin largely derives its value from future speculation. There is not much practical use for it ATM for most people. This speculation can span from anywhere between a few seconds to years, i.e. people selling on these pumps and people holding because they believe it will be worth $1,000 and more in the future.

I think a dollar collapse would cause a giant increase in the USD->BTC price and nothing else. Though I don't think the dollar will go just yet.