Kroos' absence could impact Real's midfield if Ancelotti fails to find a good replacement for him. It will be very difficult to do this fully, because he was a player of a very high level, but in time Ancelotti will cope with this task, perhaps Rabiot will take his place if he decides to leave Juventus, at the moment he has not decided anything with the extension of the contract, he left the solution to this issue after the Euro, I think everything should be resolved in the near future.
Finding a replacement like Kroos is very difficult because he has matured so much as a midfielder. But Ancelotti must find a solution so that Real Madrid remains strong and has players who are able to maintain the rhythm of the game in midfield.
Rabiot might be an option but there is no clarity regarding that so Real Madrid must try to find some suitable replacement figures.
They also have several young players who might be able to replace Kroos' role, but their skills and composure will definitely be different because their experience is not yet as mature as he is.
In the previous season, Ancelotti had implemented the scenario if they played without Kross and he had done this many times by rotating positions and sometimes Kross came on as a substitute or he was replaced. That was a preparation he made if he lost Kroos and they will feel that next season. The player who fills the void can replace his role quite well, even though he can't fully play like Kroos. But that is normal because it is a process.
At least Ancelotti cares enough and is starting to get used to the game he has changed when playing without important players who are usually always his mainstay. The scenario next season will be different, because next season Ancelotti will no longer have Kroos who has decided to retire. I think there will be a moment when Real Madrid will feel like they have lost this player, because so far he has been a player who has very good playing vision with very mature passing.