It's not a 100% that Tank is out but it looks like that will happen. It doesn't have anything to do with how Auburn used him and everything to do with a shitty offensive line. If Tank had a decent o-line his stats would be considerably different and for RBs better stats equals more money at the next level.
Honestly, I don't blame Harsin for either of these things as Nix is leaving because he is finally getting coaching and is struggling to come to terms that he isn't the golden child and that he needs to improve. I would argue that in one year under Harsin Nix actually improved as a QB especially in the footwork but I don't think he can deal with the fact that Harsin also benched his ass when he was sucking it up. We have a freshman named Dematrius Davis that hasn't seen the field this year but has made some noise. Nix is running from the competition because he was guaranteed to be the starter next year and that is the way it should be.
The o-line has literally been an issue for Auburn for the past 4 years and we have pieced together a line with key transfers year after year and each recruiting cycle it has been a priority and we have missed every year. Offensive linemen just didn't want to play in Gus's system as it didn't prepare them for the next level and that has been confirmed by NFL teams. When you don't have the talent on the line it's hard to make living as a QB.
The rebuilding really begins this year and we'll see what Harsin brings in.