After suffering a devastating loss at the polls, the Colombian government and the country's largest rebel group were scrambling Monday to salvage the peace deal they believed could end the 52-year battle between them.

Colombian President Juan Manuel Santos ordered leaders from both sides to reconvene Monday in Havana, where most of the negotiations have taken place over the last four years. The head of the Revolutionary Armed Forces of Colombia, known as the FARC, was already in Havana where he expected to celebrate the passage of the peace deal, but is now hoping to revive negotiations.

During a televised address late Sunday, Santos said the ceasefire between the government and the FARC would stay in place as they try to find a way to resurrect the defeated deal. He said he would meet with negotiators, as well as leaders of the opposition movement that campaigned against the peace deal.

On Monday, Humberto de la Calle, Colombia's chief negotiator, offered to resign from his post over the failed vote, saying his team clearly made mistakes that led to such widespread dissatisfaction with the accord. But he was summoned to Havana to continue negotiations anyway.

"The desire for peace is universal and unanimous," he said. "I will continue pursuing the objective of peace in what remains of my life."

Colombians reject historic peace deal with rebels

The problem facing the leaders is that they never developed a Plan B if the national referendum failed. Santos insisted on the national vote over the objections of some in his government and leaders of the FARC, arguing that such a historic deal needed public approval.

Now, Colombians are unsure what will come next.

Douglass Cassel, a professor at the Notre Dame Law School who was appointed by Santos to help negotiate the peace deal, said it was unlikely the two sides would scrap the 297-page accord and start from scratch. Instead, he said they could try to tweak parts of the deal that most upset voters, such as the minimal prison time FARC guerrillas would have faced and the guaranteed seats in the Colombian Congress for the guerrilla group.

With a final margin of just 50.2% to 49.8%, Cassel said it might not take much to put the deal over the top.

"It doesn't take a whole lot to move a 49.8% 'yes' vote to majority support," he said.

Another option is sending a version of the peace deal directly to the Colombian Congress, where a majority of legislators have embraced the accord. That would face major criticism from voters, but Adam Isacson said it could be done in a way where Congress approves some aspects of the deal to maintain the momentum from the peace talks.

"There are backdoor ways to get this through," said Isacson, a senior associate at the Washington Office on Latin America who was in Bogota for Sunday's vote.

Whatever the negotiators decide, Isacon said they will have to move fast. While the ceasefire remained in place Monday, ceasefires have always fallen apart during previous peace negotiations going back decades.

"They can't stay in limbo very long," he said.

Cuba and Norway, the two countries that co-sponsored the negotiations, insisted they will continue to facilitate the dialogue.

"We have told both parties that we will be at their disposal and are available," Norway's Foreign Minister Borge Brende told the NTB news agency. "We must also involve the opposition who say they want peace and hear what they think might be the solution."