They stay in jail. Sentences aren't retroactively rescinded when laws change. Edit: As the response to another post has stated, there may be avenues opened aft

They stay in jail. Sentences aren't retroactively rescinded when laws change. Edit: As the response to another post has stated, there may be avenues opened after decriminalization to appeal convictions. Those avenues will likely vary from state to state, if they exist at all.