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