A lot or a little of the Affordable Care Act could be left standing if a federal appeals court rules only the requirement that individuals buy health insurance and those provisions tied to it have to be struck from the law.

Figuring out what can stay and what must go will be no easy feat, legal scholars say.

During oral arguments earlier this month over the fate of the sweeping health law, the U.S. Court of Appeals for the Fifth Circuit signaled it’s likely to rule the so-called individual mandate is unconstitutional now that Congress has lowered the tax penalty...