Truth be told... Replacement will go to the CBO eventually, as will the repeal. In fact the House just voted to change the CBO's reporting rules. They're now requiring either 40 or 50 years' cost analysis for bills that are expected to cost over $5 billion.

....Except repeal of the ACA of course. That action specifically is not required to be forecasted that far out; instead it is only required for 10 years.

Of course nothing will prevent the CBO from showing 50 years of costs associated with repeal (which would be YUGE), but there's a reason an exemption was carved out for ACA repeal.