Like I said. The IRS goes away due to defunding and is replaced by the Sales Tax Bureau.
IMHO, the IRS is unfairly hated today. All they do is enforce the laws written by Congress. But the IRS takes the heat. So when you say the IRS is being abandoned, everybody cheers that because everybody "hates" the IRS.
However, what ever the tax scheme, Fair Tax, Flat Tax, what ever, a government entity will be needed for collection and enforcement. Call it the Sales Tax Bureau, call it the IRS, call it Incompetent Bureaucrats Doing A Bad Job, it's job will be enforcement and collection.