Xabi Alonso is prominent enough to handle the hurdles which will be coming his way next season. Remember he's the main reason behind the sudden peak form of Bayer Leverkusen, they're able to comprehend the situations at hand and hitting top target in each season. Bayer Leverkusen have relaxed their players and they're warming up for the big season ahead. This is not an easy one because the entailed actions involves other oppositions.
I also have no doubts about the ability of Xabi Alonso especially for this season again because from what he has shown last season at Bayer Leverkusen to be able to win the Bundesliga is something extraordinary so that it has been a good achievement for him and hopefully can be achieved again this season. However, I do not think that Bayer Leverkusen can easily face the obstacles in the UCL, because it is a competition with quite high tension and very different from any competition including the Bundesliga.
If you maintain consistency in implementing tactics then it is likely that it will happen, winning the Bundesliga is an achievement for all clubs in the German League and the main target to get it, of course Xabi Alonso will continue to defend the title this season with the existing players. playing in the Champions League is a bonus for every team, no matter how difficult the match and opponent faced in the Champions League I think Xabi has prepared for it and already has ideas in the tactics that will be played this season, I am sure with Leverkusen in Xabi's hands will be better than the previous season and they are certainly ready for any difficult matches.