What would happen to such a bill when it reached Obama's desk?
Defunding isn't a real solution either because Obamacare isn't just about funding. It imposes rules on third parties, hospitals, doctors, patients, insurance companies, etc., that aren't depending on funding.
The only real solution is replacing it, and that's not going to happen with Obama as president. Unless it destroys the health care system to the point where even Obama has to accept an alternative.