I don't think Xabi Alonso's proposed departure from Bayer Leverkusen at the end of the season is certain as the young Spanish manager is yet to publicly notify everyone about his next move
If Xabi Alonso leaves Bayer Leverkusen, then this will definitely be Bayer Leverkusen's final journey to become champions in the Bundesliga because the chance of winning will not happen a second time with a different coach. Xabi Alonso now knows the strengths and weaknesses of every player that Leverkusen has, so this coach is able to provide the right position for his players to bring victory. It is not certain that a new coach will be able to do what Xabi Alonso did.