NFL will enforce all applicable rules to the letter concerning Williams. They have to, basically, since he's so high-profile.
Dolphins will welcome him back with open arms with little or no hard feelings. From outside perspective the assumption is they'd be peeved. From inside perspective, they know he is (and most players in NFL are for that matter) very young, very rich, very talented, and very confident. Anyone with those properties is bound to make stupid mistakes. They think they're kings of the world and lots of 'em don't think far enough ahead. That's why they play with broken legs and mangled knees.
I see no possible way that he ever plays for MIA again. The players on that team absolutely hate him, and look whats happened since he left....
They traded a pro-bowl defensive player for Booker and a 3rd rd pick. They then traded a 3rd rd pick for Lamar Gordon, who proceeded to be put on the IR within a couple weeks and he put up 0 production. They completely wasted that pick, and the trade for Booker was a joke.
MIA was between a rock and a hard place b/c of Ricky and the organization has taken a big hit b/c of it. There is no way they trust him again. Not to mention he will probably get another substance abuse violation