He has a buyout clause for 2017 for 30m and Gladbach have been lucky, that no big club showed genuine interest before he signed the extension last year. Bayern showed interest after that and Eberl made it clear to them, that there is no chance in the near future and that he is not for sell. He is impossible to get this winter and I m not sure, if there is a chance to get him next summer. Eberl is tough to deal with and the opposite of a pushover. One thing is clear, the amount must be considerable higher than that 30m€.
I think that Bayern r still very interested in him and want him to be the Alonso successor, but the 1 year extension of him makes it unlikely, that they ll go for Xhaka next summer. Maybe Bayern know more that he isnt gettable next summer? Then u also have to compete with the usual EPL clubs, who have also showed interest. It ll be again a tough fight to get this fella.