I picture it this way. Barnes is a known bad arse bad guy. After losing to Daniel, him and Silver were completely disgraced and broke. Him / they ran off to Central America / South America / Mexico and get caught up in drugs / cartels. Silver builds himself back up (as we've seen in season 4) and we know he isn't beyond illegal stuff (as we've seen in KK3). Barnes builds himself up as a big drug guy (why else would Miguel's mom have run away and been so scared for him to going looking for dad?). Silver said he was gonna "dig up somebody to help", so Barnes is the obvious choice. The more I think about this scenario, the more I think that it's going to play out pretty close to what I imagine. Maybe I'm totally off base, though.