I agree with you that the decision to leave or stay is a double-edged sword, on the other hand this is an opportunity to change fate and career to a high level, but it all depends on Xabi decision between leaving this zone or staying. and the possible difficulty of finding other opportunities. In my opinion, Xabi should stay longer at Leverkusen to prove that there he really has a big influence on the team's performance, not just luck. Xabi does have the qualities of a great coach. 1 more season with Leverkusen is enough and he can accept the offer.
If he received a good offers from other team, why he need to take a risk to prove himself for two seasons lol. It's either Fernando Carro increase Xabi Alonso's salary and give him privileges or Xabi will move to other team.
There was an interview by DAZN, it looks like Carro doesn't look want to give a special treat to Xabi, so I believe he will join other team.
"We're happy that he's here, but Xabi Alonso is a puzzle piece. It's not like everything will fall apart when he's not here," Carro said in an interview with DAZN.