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This would amount to an increase in money demand, which will raise the world interest rates, lowering output(GDP). In other words, yeah it could but this wouldn't just affect the US. The debt market really is global, China can't demand it's money back (think fixed terms of loans). It can however, decide to limit theamount it loans in the future. This will raise interest rates in the US. Thse outside the US will see higher rates and lend there money to the US in hopes of greater returns, lowering the rates in the US to the world rate (which will increase because of the rise in money demand).
Oil consumption is greatly elastic at these amounts. There is a $ per barrel price that will make the construction of a decent public mas transport systemin the US. [insert many other industries that will flurish in the face of highoil prices] In the best case senerio, we will have some inflation and emergance of new technology. The worst case senerio is much more extreme...
Social security is simply a redistribution of wealth. This won't cause a depression. In fact, having it around is much more likely to cause a depression than not.
[I'll assume you mean close to 100% ]This can actually cause some pretty wierd stuff... You will see zero imports to the country (foriegn goods will be very expensive) and massivly huge amounts of production (real GDP). Again, this would be difficult to happen because of effects of globalization.
Interests rates will rise... but it really depends on the type of unemployment.
Yes, under any circumstance it's wonderfull to own your home outright.