By Helen Murphy and Luis Jaime Acosta
MEDELLIN, Colombia (Reuters) - Jessica Quintero awakes drenched in sweat and instinctively grabs for her AK-47 assault rifle. With her old weapon no longer there, she hides beneath the sheets to escape the air raid of her nightmare.
"The bombs still scare me, I don't sleep," says Quintero, 18, recounting a regular night-time ordeal after fighting for three years with Latin America's oldest guerrilla group, the Revolutionary Armed Forces of Colombia, or FARC.
Scared of the persistent air strikes on her camp deep in Colombia's jungle, the former child soldier fled and surrendered in 2013, one of thousands who abandoned the FARC in the last decade as its ranks were cut in half to around 8,000.
Quintero, whose 11 siblings also joined the rebels, now spends her time with 60 ex-combatants, receiving post-traumatic stress therapy at a safe house in the city of Medellin.
They are trained in car repair, sewing and electrical wiring, while learning to read and write.
President Juan Manuel Santos hopes to incorporate thousands like them into society if peace is reached at talks with FARC leaders in Cuba that have gone on for two-and-a-half years.
But combatants face multiple challenges. Many like Jessica have been traumatized by war, others have spent most of their lives fighting in the jungle and have few other skills, and Colombian society might struggle to accept them.
If the reinsertion policy fails, there could be additional suffering for Colombia after 51 years of conflict as former fighters struggle to find jobs and a new life.
It could also crimp growth in Latin America's fourth-largest largest economy.
Crime gangs are already recruiting at safe houses, says Jonathan Lucumi, 19, a former insurgent who has been approached to sell drugs for good money. Others are enlisting, he says. "They're keen, they love their guns."
The criminal gangs, known as Bacrim, gained strength in 2006 after the demobilization of right-wing paramilitaries - bitter FARC enemies - failed to incorporate the roughly 30,000 into society. About a quarter of them turned to crime and the gangs are now Colombia's biggest security threat.
Most Colombians hate the FARC - the war has killed about 220,000 people - and may be reluctant to employ or welcome them into their communities, as happened with the paramilitaries.
"FARC are attractive to the Bacrim because they can handle a gun," said Olga Garcia, who helps former rebels at the safe house. "They can't put FARC on their resume."
The government believes a "peace dividend" could bolster economic growth a couple of percentage points, although some academics see a "peace paradox" if former rebels take up crime.
"While the cost in terms of GDP associated with the conflict is reduced by peace, the cost associated with organized crime could increase," says a study by the Sabana and Javeriana universities and conflict think-tank CERAC.
That may be avoided if private companies employ ex-combatants, and the Chamber of Commerce says about 80 percent of Bogota-based companies are willing to help.
Some, like Coca-Cola Femsa, have been involved for years, offering courses to about 1,600 former rebel combatants and hiring a few at its Bogota bottling plant.
Colombia spends - and will spend after any peace deal - about 4 million pesos ($1,500) annually in education and work training programs over 6-7 years helping combatants return home, said Joshua Mitrotti, of the state's reintegration unit.
Jail costs triple that, he says.
"It's not just reinsertion, it's reintegration - a total transformation of the individual," said Mitrotti, estimating success could take six years.
But independent organizations, like the safe house in Medellin, say the government is way behind and is underestimating the costs involved. Three million pesos are needed monthly per person for at least three years and dozens of rehabilitation centers established nationwide.
Many former fighters feel stigmatized.
Carlos Gomez, 51, left the FARC and completed the government program, receiving 8 million pesos to start a small business. But he lives in fear of being discovered.
"I'll be judged, or worse, if people know my past," he says, speaking out of workers' earshot at his small garment factory.
Many Colombians agree.
"I want peace, but I'm not ready to interact with FARC," said Bogota dentist Adriana Jimenez, 38. "I don't want them to live near me, or their children to play with mine. They could be dangerous."
While the government wants rebels, who mostly come from poor rural backgrounds, to return home and build lives farming, that will be difficult.
Some 60 percent of Colombia is undeveloped with rural development years and billions of dollars away. Poor roads make transporting crops costly and the oil industry, a major driver of growth, has recently faltered amid price declines.
Coca cultivation - a lucrative FARC business - would be difficult as authorities quell cocaine production.
Past demobilizations have brought mixed results.
The 2,000-strong leftist M-19 successfully disarmed in 1990 and ex-militant Gustavo Petro is now Bogota's mayor. But Antonio Navarro Wolf, a M-19 leader turned politician, warns that peace accords often "swap one type of violence with another."
Some 5,000 sympathizers of the Patriotic Union, a party founded by the FARC in 1985 as part of peace talks that ultimately failed, were murdered by paramilitary death squads in the following years.
"There's never been a peace process when rebels haven't been killed," said Senator Ivan Cepeda, whose Patriotic Union father was gunned down in 1994.
(Reporting by Helen Murphy; Editing by Andrew Cawthorne and Kieran Murray)