I assume that if Real Madrid can't find an alternative, maybe there will be compromise for one more season with Ancelotti. But he knows if he wants to prepare the Brazilian team for 2026, he can't wait any longer than until summer 2025. I am sure that coaching a national team at a World Cup is one of his big plans and getting the chance to take responsibility for the Brazilian team sounds like a great opportunity. But if he doesn't give it enough, time it might go wrong big time.
After joining in 2024 he will be going to prepare things for the 2026 world cup which is surely not easy because he needs to start from scratch and also needs to be having well preparation for the qualifiers as well because currently they are not good which is also problem for them in near future.
I said that the deal seems to be "pretty safe" for a reason and that was because I couldn't find any sources definitely calling the deal "safe". Interest has been expressed from both sides from what I understand, but so far there hasn't even been a handshake confirming that this deal is sealed. If anyone knows a reliable source where we can read upon more reliable information about this agreement, I would like to know it. But this could still go in different ways when Real Madrid has no alternative and tries to convince Ancelotti to stay for one more season. I think there are less attractive jobs than being the coach of Real Madrid.