President-elect Trump and the GOP-controlled Congress can repeal Obamacare pretty easily, but the biggest question is when and if there will be a transition while a replacement gets crafted.

Trump has promised to repeal Obamacare in its entirety and congressional Republicans are on board. However, when the repeal would take effect is largely in doubt, as some Republicans are wary of immediately ending coverage for millions of people without a replacement.

Trump said Friday during an interview with CBS News that he would immediately have a replacement for Obamacare after it was repealed, and there would be no gap between the two.

"We're going to do it simultaneously. It will be fine," he told CBS Evening News. "And we're not going to have, like, a two-day period and we're not going to have a two-year period where there's nothing. It will be repealed and replaced."

In the Senate, Republicans can use a procedural move called reconciliation that enables them to avoid a filibuster and pass a repeal bill through a simple majority vote. The GOP holds a two-seat majority in the Senate and could repeal the law soon after Trump takes office in January.

The reconciliation bill did include a two-year transition period that would keep the exchanges and subsidies in place while a replacement was crafted and passed.

However, a replacement for Obamacare could take longer to implement, and some say that means an uncertain future for the law's exchanges and the millions who get Obamacare coverage.

Experts are confident that the Obamacare exchanges will continue to offer coverage throughout 2017, even if the law is repealed on day one.

"Nobody has a crystal ball but I think for the most part people can plan on having their exchange coverage and subsidies in 2017," said Cynthia Cox, associate director of health reform and private insurance for the nonpartisan Kaiser Family Foundation.

"I would expect that for 2017 we are not going to see major changes," added Sandra Hunt, a principal with the consulting and research firm PriceWaterhouseCooper. "There might be some tinkering on elements but it will take some time to really think through exactly how to address the issues that are part of the ACA perhaps."

The question is what happens in 2018?

While repeal would escape a filibuster, any replacement plan would likely have to get Democratic support to move through the Senate.

Any two-year transition period would keep in place the 2018 open enrollment, but some experts question if insurers would want to stay along for the ride.

"Health plans have stayed in the market because they are hoping it is going to stabilize and they see it as a long-term opportunity for their business," said Caroline Pearson, senior vice president at the consulting firm Avalere Health. "If that is going away and health plans are actively losing money in the market there is very little reason for them to continue participating in 2018."

Insurers are already leaving Obamacare markets due to high financial losses.

UnitedHealth, for instance, said it is leaving a majority of the 34 states in which it offers Obamacare plans due to estimated losses of $600 million from the exchanges.

A report from the think tank Commonwealth Fund found that in 2014, the first year Obamacare's marketplaces went online, showed that in 2014 only one-third of Obamacare insurers turned a profit.

Insurers generally underpriced their plans and then enrollment wasn't as much as expected and the people who did sign up were sicker than expected.

About 10 million people paid for Obamacare in the first half of 2016, and more than 80 percent of those people got subsidies to pay down the cost of insurance. The administration hopes to get 13.8 million people to sign up for 2017 open enrollment and have around 11 million pay their premiums.

Going into 2018, if insurers see more instability in the exchanges then they could exit the exchanges altogether, Cox said.

"There needs to be some sort of plan in effect before open enrollment begins in 2018," she said.

It could be that insurers continue to take a wait-and-see approach, Hunt said.

"I think that most insurers who want to participate in the market are probably going to assume no change and wait to find out," she said.

But, unlike the repeal of Obamacare, implementing any replacement plan will not be easy, no matter what Republicans decide on, said John McDonough, professor at Harvard T.H. Chan School of Public Health.

"Let's assume they get something done by the end of 2017," McDonough told the Washington Examiner. "They will have to go through a whole regulatory process to write the rules for this whole system. They can't just take the statute and put it in place."

Every piece of regulation will also require comment periods of two months or more, he added.

Obamacare, for instance, was passed in March 2010 but it took more than three years to set up the law's exchanges.

Trump's healthcare plan includes letting insurers sell plans across state lines and boosting funding for health savings accounts.

House Republicans introduced their own healthcare plan earlier this year that provides some more details, but does include letting insurers sell across state lines and boosting health savings accounts.

Speaker Ryan's office didn't say whether any repeal efforts, which he has called a top priority for the new Congress, would include a transition.

"House Republicans are only just beginning to talk with President-elect Trump and Vice President-elect Pence about the agenda for 2017," spokeswoman Ashlee Strong said. "Speaker Ryan intends to continue these discussions with the transition team."

A senior Trump campaign aide says provisions Trump wants to leave in have all been part of previous revision plans proposed by Republicans.

There are methods that Republicans can take to keep insurers around in 2018 and possibly in 2019, McDonough said.

Chief among them is offering reinsurance, a program that forces insurers with high profits to redistribute those profits to insurers with heavy losses. Reinsurance was part of a series of programs that were in place from 2014 to 2016 in Obamacare to help insurers mitigate the new marketplace.

If nothing is done however, then it could lead to millions of people losing coverage due to a death spiral in the marketplace, Pearson said.

"The notion that the exchanges could collapse under their own weight in 2018 barring any changes is a reasonable risk," she said.