Defund it how? If Obama vetoes it, we will be on a continuing resolution. The law will still move forward in terms of implementation including setting up the IPAB board, instituting the new taxes, insurance exchanges, penalties for those who don't have healthcare, employers and individuals, etc.
The problem with Congress is that we do not have a veto proof majority. Obama will implement the new law. There is nothing to prevent him from doing so.
When the debt ceiling is NOT raised, the GOP is afraid of the RAT media. There is NO USA default if the debt ceiling is not raised UNLESS THE ZERO ADMIN chooses there to be a default at the expense of all his socialism program payouts. The USA has enough monthly income to pay all the debt owed on bonds and T bills. It won't happen by choice because the GOP is spineless and will not swallow the medicine needed to right the ship of state.