What the point is for me is sell him get the money and find someone who likes the club and will give his 100 %.Its a risk keeping Lewandowski and think that he will try his best to Dortmund that blocked the transfer to the club he wants to go.He doesnt want to renew its his choice nobody can press him to do it.
Dortmund said quite a few times how Lewandowski is important to the club to do well next year in their league. We're not talking about some striker, we're talking about one of best in the world in my honest opinion and Dortmund think the same.
Sure, Robert would prefer to move to Bayern, but he didn't show so far any clue that could leave people thinking he would do crap on purpose if he does not. He said himself a few months ago that he is a Professional.
I really like Lewandowski since i watched dortmund's matches last year and I think Dortmund is right when they think he's a real diamond.
Dortmund also said, IIRC, that they don't need money and prefer to keep him and win trophies this year if they can, rather than sell him and buy a not as good striker.
Also, look at the market, there's no striker at the level of Lewandowski on sale.