For years, the Obama administration said the health care system as constructed by the Affordable Care Act could not survive without a mandate that most Americans have health insurance. With surgical precision, the sweeping tax bill that Republicans plan to pass this week will do away with that mandate.

What comes next for health care seems to be anybody’s guess.

The demise of the Affordable Care Act’s mandate will lead to higher premiums and lower enrollment in plans sold on the health law’s marketplace, Wendy K. Mariner, a professor of health law at Boston University, said Monday. But she added, “I don’t think we can say with any confidence” how much premiums will rise or coverage will decline.

The Republicans’ move came as something of a surprise. Democrats rejoiced when they defeated multiple Republican efforts to dismantle the health law this year. But Republicans have never wavered in their opposition to the mandate, which they see as a symbol of government overreach.