The plain reading of the law is that this has to flow through states not government. The GOP should prepare to offer an alternative to people who lose subsidies. Republicans should come together for a reform that makes sense that allows people to control their own dollars and replace the ACA state by state.
If the plaintiffs win King v. Burwell, it will only be poetic justice. A massive, unpopular, and largely unread bill re-shaping nearly 20% of America's economy was rammed through Congress along purely partisan lines. Since then, the Administration has re-written the black letter of the badly written law to suit their political purposes. A rebuke from the Court - that Congress should have to live within the plain meaning of the text it passed - would offer a much needed return to the rule of law.
Contrary to the claims of the administration and some commentators, Republicans have serious, realistic ideas ready to go should SCOTUS strike down subsidies in King v Burwell.