Considering what Xabi Alonso have achieved so far with Bayer Leverkusen, he doesn't need to stay many more years T the club to prove that he's a good manager. For someone with his little number of years in coaching, it's absolutely rare to achieve the great feat he's achieved so far with the Bayer Leverkusen team. A lot of European big clubs already have confirmed that Xabi Alonso possess the qualities of a great manager in his very young age and that's why many of them are seriously trying to get his services on permanent basis.
Big European clubs like Bayern Munich Liverpool and others are rumoured to be among teams that are monitoring him and that's why I think it'll be very difficult for the management of Bayer Leverkusen to still retain his services beyond the current season. Xabi Alonso have made it clear that he's a young coach with great coaching potentials and surely succeed in any big club if you ask me
there is nothing wrong if Xabi will stay longer to prove to everyone that he is truly a great coach and can help Leverkusen to achieve higher achievements every season.
after successfully winning the bundesliga title, in the end, Leverkusen management will think that Xabi is the right coach to bring big changes to the team, so whatever happens, the management will definitely try to maintain it and for Xabi, of course he also thinks that after succeeding in providing this success without being defeated, he will definitely try winning a higher title took Leverkusen to a tougher level to win the UCL title next season.
as we already know, Guardiola has survived and been defended by Man City for a long time and finally last season's satisfactory results were getting 3 prestigious titles which proves that Guardiola has intelligence when it comes to managing Man City players and it is possible that Xabi could do what Guardiola did. so I would say that in a few seasons Xabi will not leave Leverkusen.