Mutual decision. That sounds like he is definitely done.
If so, I am glad. I got no hate for him personally. And I hear he's a good dude in the locker room. But some of his comments have put me off -- he gets testy with fans on twitter, defiant about his play (I for example like Lattimore owning up to not playing hot, you don't get that humility from Brian). I hated the bullentin board material he gave to the Eagles last year, and did the same for the Lions this off season.
He's also a bit of a hipster fav for dudes I respect like Logan Paulsen and Mark Bullock who like to say he's much better than fans think, and is their best running back -- but lol, I get a bit annoyed by their arguments and I like both especially Logan typically. But I've disagreed with their take on Brian.
And on this board, I argued plenty of times why I'd love to see Brian go and got a little (not much) pushback.
The argument about Brian that I disagreed the most with is the idea that he's a good big back, tough runs, but the poor sap doesn't have breakaway speed. If that was who he truly was, I'd want him on this team. I like good-great power backs. Brian IMO isn't that. Actually ironically his athleticism for his size is actually good. He's a good athlete. But he's a pedestrian power back without breakaway speed. As a power RB, purely as a power guy IMO, he's so so. I think he has underrated hands -- if I had to pick a superpower of his, its not using his size to power runs, but he catches well.
I posted this off season some stills of clear cases of Brian having opportunities for big runs and he just didn't see it. His vision IMO is poor.