Definitely attitude and desire will be key. As it is with all our talented young players. If at this point Dier, Alli, Kane or Wimmer stop showing the right attitude and desire it will hugely hamper their careers.
If there have been problems behind the scenes I wouldn't put it past Pochettino to make Bentaleb work his way back into contention by proving himself in training over an extended period of time.
He was certainly not average last season and I don't think he was costly either. In a team lacking a lot of the ingredients from this season he was a regular starter in the team that saw us finish 5th. The system is a bit changed this season, but there are clear similarities. He hasn't been fit for a good period of this season, and when he has been he hasn't been on form. Not sure what chance he's had to push on to be a good part of the system this season...