I'm sure Bayern would like to have Manzdu on the bench as a safety but they already have Pizarro committed to another year and have the false 9s like Muller and Gotze and Robben and would probably be glad to cash in on him now, after his great season and decent WC rather than wait it out. Mandzu would cost half of what Costa would.
I think he wants to stay and until we sign a replacement he won't be moved. I'd take Khedira over Mikel, too, but I also wouldn't mind signing him and letting Mikel stay as cover, either. He hasn't complained about playing time and I can see him contributing with 10-15 appearances.