It is inevitable that the U.S. will hit a depression far worse than the great depression.....whether or not there is an extension. The extension will just put it off just a little longer.
If there is no extension, then when the 5 mil. people lose their unemployment it will begin a snowball effect where their money is not going into the economy and will lead to even more job losses. As the unemployment runs out things are going to spiral down quite fast and then this country will literally become bankrupt.