I have no idea why anybody thinks BVB would swap Reus for Alexis or sell him for 30-35 mio. €.
Unless they can't get his buyout clause removed, they'd most likely rather lose him after the next season for the buyout clause of 35 mio. €.
They'd only be tempted to let him go before next season if somebody would offer outrageous amounts of money (think along the lines of 55 mio.+) or offer a similar player, someone like Alexis, plus 15-20 mio. I doubt however, that someone like Alexis could be convinced of playing for BVB/in Germany.