The most likely outcome:
For a while in Colombian and American media there will be a collective prophesy that FARC is in super deep water or about to come to an end, then in a few Novembers we may very well have a scare in some circles like the one circa 1998 that FARC is going to take power in 5 years, which will prompt a whole new round of military aid to America's favorite Latin pet. Then some bigshot in FARC will die, the media will praise it to the heavens and herald a new age of peace, some lower member of FARC's command structure will take the position, their leadership will shuffle around, and the status quo in Colombia will continue to go on for god knows how many years. This isn't the first time FARC has had some head honcho killed, nor is it the biggest blow ever.
Alternatively, this assassination might actually be the super special silver bullet that causes the rebellion to unravel.
That's not likely though, because the FARC is one of those groups that goes through leaders like the Romans went through emperors.
We're all disillusioned with capitalism.