If the dollar crashes to ground zero, it will further push the price of Bitcoin higher and occasion the a rise in demand level for the coin. And I don't see such affecting Bitcoin in a negative way. Rather it will bring about an unnecessary hype in its value. Mind you, dollar isn't the only internationally accepted currency of the world. It isn't even the highest currency too.
Yes dollar is just universal currency, and all countries accept this dollar, but apart from this, we have many valuable currencies in this world. And the value of those currencies is higher than this dollar. So if the dollar price goes down, then BTC value will be calculated by other reputed currency. So the value of the BTC will not effect.