Surely,United don't have anywhere to play Kagawa.They have Mata and if he doesn't start,Rooney for that position.However,I do think that he will prefer moving back to Dortmund if he is to leave.However,after signing Shaw+Herrera for 70 odd,I think United would need to sell some of their bench warmers to get new signings in,especially if they are to invest further in cb,who aren't exactly the cheapest in the market right now(Marquinhos,Luiz,etc.)
Making United agree to a 15-20 mln could be done.Making Kagawa accept us is altogether different,especially with no Conte.