It's such a shame that the NFL has the ignorant MJ-prohibition stance that they do. It's racist, quite frankly. Alcoholism does thousands of percent more damage to society yet NFL players can get drunk as hell all they want so long as they don't drive or beat their women. Show me a guy who plays well on Sunday, gets to practice everyday, and stays out of trouble, and I don't care what the hell else he does. The NFL is joined at the hip with the corporatocracy that rules our world and the corporatocracy has huge financial incentive to push MJ prohibition, from Big Pharma to the prison-industrial complex (and law-enforcement and gun sales industries) to the alcohol manufacturers and distributors themselves. MJ prohibitions is fascism in a nutshell.
So, with that said. The rules are what they are and Blackmon ('Da man keepin' the Blackmon down') could likely get himself permanently banned. If he didn't have the discipline to abstain the last time, after already missing 4 games, then I don't see him having the ability to abstain in the future.
I'd love that talent though. It's Josh Gordon/Brandon Marshall level talent. If he's there, you grab him...but not with that weed situation lingering like that. Can't do it. Another team can do it and everything would work out. You just know, though, that if the Dolphins tried it, it would immediately backfire. He'll wind up being the next Randy Moss for the last 2 years of Brady's career.