I agree that a debt based society is not sustainable; however, who would you picture this collapse?
In my opinion, this is something that would have to take place over decades. If the USD collapsed, then social security, car loans, house mortgages, college loans, the financial systems, everything would be wiped out.
There is just too much money on the table for the government and large businesses to sit idly by and allow that to happen.
I view it as a slow change. 1st people will chose not to use USD and opt for say Bitcoin. As the revenue is leaving the debt based economy, businesses will begin to embrace Bitcoin (Money flows where it is treated well). As more and more people transition over to Bitcoin, the problem will slowly fix itself.