Why Does There Have to be a Replacement to ACA?

Eli,

I know the Republicans have stated they will "replace" the ACA, but I don't see why they should. When natural gas prices were deregulated, there wasn't a replacement. When airlines were deregulated there wasn't a replacement. When wage and price controls were eliminated after WWII, there wasn't a replacement. When wage and price controls were eliminated in 1975 there wasn't a replacement. I don't see why there has to be a replacement to the ACA either.

Bill