If Leverkusen extends the contract of Xabi Alonso they will not let any other teams including Liverpool or Bayern Munich even think about their coach to hire Xabi Alonso for the next season. But the fact about Xabi Alonso and Leverkusen is they are going to play in the Champions League for the next season and if they have Xabi Alonso, they will be a strong team in this tournament. However, I think Leverkusen will also need to hire some players and get improve to make them ready to play against stronger teams like Real Madrid.
Sadly we don't have Leverkusen in the Champions League in this season, but I'm waiting for it until the next season.
Leverkusen would definitely extend Xabi Alonso's contract after his latest statement on his future.

He clearly stated that he was ready to go longer with Leverkusen. This will be enough to drop the interests from Liverpool and Bayern Munich quickly. Leverkusen are about to join the Champions League group stage officially.
Xabi Alonso would really make use of some good additions to strengthen the squad this summer. Because the Champions League arena is much tougher than the Bundesliga. If he wants to achieve the best they can there then this is a need for them.
Basically Bayer Leverkusen did not try to extend Xabi's contract but, in fact, Xabi himself has to stay one more season at Bayer Leverkusen. With his statement, then of course it becomes clear that Xabi is free to choose to stay or leave because after all, Bayer Leverkusen itself has stated before a few months earlier that Bayer Leverkusen is ready if Xabi chooses to leave and will not hold him back. Therefore, at least Xabi Alonso can still show a loyal attitude to the Bayer Leverkusen team, even though his career is on the rise but Xabi does not seem too crazy about money. Because of course, if Xabi chooses another team, then of course Xabi will get a bigger fee such as choosing Bayern Munich or Liverpool. But indeed, it will be interesting about Xabi's choice to stay at Bayer Leverkusen, of course, next season will also prove whether Xabi will still succeed in providing very impressive results for Bayer Leverkusen or not.