I believe Xabi Alonso is the sole candidate for the managerial job at Real Madrid based on his achievements with Bayer Leverkusen in such a short while as coach of the German side. But this doesn't necessarily mean that if he eventually gets the job that he would perform the same way he has done with Leverkusen. In Spain it could be very difficult due to pattern and the tempo of the competition in the Spanish La liga.
Moreover being the coach of Real Madrid comes with lots of responsibilities including consistency, which means if you fail to be consistent for a very long period of time then you might be shown the way out because at Real Madrid they have a very slim tolerance for failure. So if Xabi Alonso finally takes up the job then he should be ready to face all challenges involved.
There is no point in discussing this, because Ancelotti is not going to leave the team, he has gone through difficult times for Real with dignity and now they are leading La Liga and in the Champions League they are only one point away from the top 8, I think they will win the match with Brest without problems. So Ancelotti will definitely do everything to defend the title of champion in La Liga and the Champions League.
I can boldly say that Ancelotti will be able to defend the title in Laliga and not in Champions League, because Barcelona is a big problem for them. If Real Madrid clashes with Barcelona, Barcelona will knock them out, because Barcelona is superior to them this season. We have seen how the match ended twice that they clashed this season.
Barcelona scored nine goals against them in two games. Real Madrid could only score two goals against Barcelona. Even though Real Madrid is the leader in the league, Barcelona has become a pain in the neck for them. If Barcelona matches Real Madrid in the Champions League, I think there is a possibility that Real Madrid will be eliminated. Also, such an elimination could even be like an early final. However, Real Madrid is playing exceptionally in the Champions League. Maybe Real Madrid can play better in the match they will play in the Champions League.