People wouldn't be able to exchange USD for BTC, so bad.
Ill trade you a quarter bitcoin for that nice boat of yours.
See how easy that was? No dollar or banker needed.
What if he doesn't want btc for his boat? That's the inherent problem here. BTC isn't accepted in the mainstream world so that guy would be an idiot to take your BTC. Unless he saw an opportunity to exchange the BTC for USD. Still haven't changed anything because in the end it's still about the dollar.
This is all assuming bitcoin becomes a mainstream currency. I know, you wouldn't bet a satoshi on that, but a lot of us are banking on it.
For that matter, what if he doesn't want dollar? He won't, cause it will have collapsed in the scenario in question.
Barter is inefficient. A new form of money will be created when the old order dies. Nothing to worry about, except for fiat bagholders.