This is one of the most painful intersections of criminal justice and changing law. A 30-year federal sentence for marijuana, even with conspiracy attached, reflects how aggressively the federal government prosecuted drug offenses during certain periods, and the contrast with today's legal landscape is stark.
On the legal question: federal legalization of marijuana would not automatically release anyone currently serving time for marijuana convictions. Laws are not typically retroactive in that way without specific legislation authorizing resentencing or clemency for people convicted under the old standards. Congress would have to pass something that explicitly addressed the status of people currently incarcerated for marijuana offenses, and the executive branch would have to act on it through pardons or commutations.
That said, there is precedent and momentum for exactly this. The First Step Act in 2018 did allow retroactive sentence reductions for certain drug offenses, and the political conversation around cannabis justice has grown significantly. Organizations like the ACLU and various drug policy reform groups are actively working on clemency campaigns for people serving long sentences for marijuana. His attorney should be tracking any developments in this space closely and filing motions if and when new relief becomes available.
With 12 or more years still ahead, anything could change in the legal landscape. It is worth keeping an attorney engaged and watching for any federal action that could create a path to early release.