I'll answer the question (I'm a little late to the party.)
The answer to the question "what will happen if we stop spending the money we do not have." is "the same thing that will eventually happen to us if we continue to spend the money we do not have." The only difference is of time and degree.
Like many have said, borrowing can be a useful tool to creating and expanding wealth. Borrowing as a permanent policy will ALWAYS lead to disaster. Borrowing to increase capital can be good as long as allowances are made for the risks. Placing your mortgage on a Credit Card is another thing entirely. Right now we are to the point where we are using a credit card to make payments on the credit card that we are using to pay our mortgage. That is not sustainable no matter how much money you think you can print. Money only exists because people have faith it is redeemable at a stated value. If you lose that faith, currency is worthless. We are approaching that level.
I lived in Russia in 1997. It cost 2600 rubles to buy a bottle of Coke. Imagine that your promised pension payed out at 5000 rubles a month. It was a good deal in the 70's and 80's. Not such a good deal when your currency collapsed. I watched 80 year old pensioners selling onions on the street because their safety net had collapsed. Russia was a superpower. To think that that same thing cannot and will not happen here is rediculous.
So yes, we need to make some heavy changes right the Hell now. First thing we need to do is elect people that have actually balanced a budget and understand the concept at all levels of government.
Next, we need to institute a 5% accross the board spending cut on all departments. This isn't the entire answer. This is just something to do while the heavy machinery is put into place. These will be real cuts, not just a reduction of the increase in spending.
While that is happening, the tax code needs to be renovated. The tax code needs to be flat removing all deductions. The tax code needs to become a source of revenue generation, not social engineering or a way to pay back your supporters. A flat tax code eliminates most of the graft.
Meanwhile three independent firms need to audit each government agency. 25% of these agencies need to be completely removed based on the findings presented.
Social Security needs to be decoupled from the general fund. A good way to do this is to use mineral rights taxes from the new oil reserves found on public land exclusively for the social security trust fund. The money from the oil and gas reserves will go into the trust fund and not be touched. As the fund fills up, we would stop the SS tax on the youngest first untill it is eventually removed from everybody.
We see where we are at. If we are running in the black at this point, we sell federal land to make up much of the federal deficit and pass a balanced budget amendment.
Additionally no more bailouts for anybody ever. Especially stupid states like Illinios and California.
A whole lot of suck for everyone there. The current people in power contributed to a larger part of the mess, so they should be the ones to suffer a bit to fix it. Anyone who thinks it is OK pass this crap off to our children wdeserves multiple, daily kicks to the Jimmy.