And which crimes should they go for? Guns aren't needed when you don't need to defend a territory. Smuggling would be an obvious next step, but what should they smuggle? Diamants? Counterfeit goods? Women?

All those are much more difficult to smuggle than drugs and the price per kilo is much, much less so they would have to invent new ways of smuggling. At present drug prizes it makes sense to build one way semi-submercibles (or even submarines) to get the stuff from Columbia to the US, I doubt the risk is worth it if you are to smuggle counterfeit goods at a few dollars a pound.