I wouldnt doubt youd see them disband to a certain extent but to think the ppl in them wouldnt still be a problem is ignorant.
Look at what happend in columbia after escobar got killed. The amount of crime sky rocketed b/c there wasnt anybody there to keep it in check. Probably be alot of the same, instead of a large group of people that has to report to a few small ppl you would have smaller gangs like you said but more crime all together.
what makes you think that crime wouldnt be in teh US like it is now? but even more so since their would be smaller gangs and less ppl to report to.
Of course they won't go away completely, nothing ever does of this nature. However, removing their prime financial motive would erode them into entities unlike anything that they've mutated into now, which is WAY better than the alternitive.
It's not our job to police Mexico, local crime is their problem, but when they directly affect citizens of the United States then they should suffer the full wrath of our military. If legalization isn't an option, then a clean sweep of the cartels and put into place people who will work with us, not against us.