Watch to see if there is any legal action to reduce his suspension. As far as I know, the Vikings can't do anything with him until he is not suspended, which really hurts because they can't even negotiate his contract. And all speculation points to his contract (and his willingness to restructure) being key to whether or not the Vikings keep him on. If there isn't any legal action, and it starts to look like he will get the all clear in April, watch what the Vikings do in free agency (starts March 10th, I believe). Remember, April is just the "earliest" he can be reinstated, so it could drag on longer.
All in all, it's going to be a lot of speculation until he is actually reinstated, unless someone comes out and specifically says yes or no on his status. But we all know how likely that is to happen. I know the players/coaches all seem to want him back, and all reports indicate that the front office would also welcome him back. The big questions really are, will the Vikings pay his salary or if not, will Peterson restructure to stay here, rather than take his chances in free agency where he very likely would make even less (his market value is still likely highest in MN.)
