I agree with you. Real Madrid will go all out to beat Barcelona. I think this will be an important moment for them because if Madrid is able to beat Barcelona then they will be 11 points ahead of Barcelona in second place. This will further secure first place for them. The Champions League will be played on May 1. That means Madrid will have sufficient rest time after playing Barca. The next match is against Sociedad before the first leg of the Champions League. I think Ancelotti will try to focus on El Classico and will rotate players against Sociedad.
Ancelotti is still able to rotate players in every important match to prepare their squad for more important matches in other competitions each season. This means that Ancelotti really understands their current condition so he knows who to place in matches that will not affect their position in the current standings. But for the El Classico match, of course Real Madrid will try to win again at home in order not to feel embarrassed by their own fans because it would be a very big prestige for Real Madrid if they had to lose to their arch rival at this time.