Plenties of names available in the market, and are you still worrying Madrid can't find someone who can perform as good as Ancelotti? There are some names available to be signed by them such as Xabi and Iraola. It may take a few weeks for Madrid to find someone who can suit them well like Ancelotti did. Why do we need to feel worry about that?
If Madrid still gets huge success under Ancelotti, they should defend him. However, i have heard they are ready to partways with Ancelotti if this season doesn't meet their expectation.
I also assume different coach, different policy regarding the development of young talents.
No one can deny the quality of top coaches like Carlo Ancelotti but whenever things don't work good, the time to get some fresh air came and it would be better to change.
From what I saw, there is Pep Guardiola who is in a worse situation in Manchester City than Ancelotti in Real Madrid and a switch between these two would be a great opportunity for their players and teams. However I doubt Guardiola will go there and face Barcelona's fans.
For Xabi Alonso, I think it will be a good chance for him to train and win something with Real Madrid and I think he might be a good one. Same goes for Arteta in my opinion.