It would be very surprising if Real Madrid had to make a big mistake that would open up opportunities for their rivals to continue competing with them until the end of the season. The reason is that with the range of points they have now, they should be able to focus more on each match so that they can always secure 3 points from the matches they play. They cannot afford to make any mistakes that will cost them points, my draw will keep them closer to their rivals this season.
Ancelotti must be able to ensure that his current team can always perform optimally in every match. Every match towards the end of this season is a very decisive match, and they must be able to win the title as soon as possible, so they can relax more. The reason is that they also have a very difficult match in the Champions League, where they have to face Manchester City in the quarter-finals. It won't be easy for them to beat Manchester City, they even have a smaller chance than their opponents in the Champions League.
What you said might happen in this stage of this campaign with them coming back from the international break and getting prepared for the champions league is something that can happen that's dropping points. In as much as Madrid are topping the league with many people thinking or have predicted that Madrid are champions already an upset might happen, like Madrid not only opening a way but dropping more points, starting with there first game after the international break.
They might lose like 3 games or draw them for either Barcelona or Girona to take there spot on the log, it can happen especially when the break is over you see bigger teams messing up, it's expected.
Fatigue will hit on players and when that happens there performance won't be as expected and you'd agree with me that Madrid have so many injury prone players in there first team so if that happens it will affect the team and I even see them being desperate in getting a win in any encounter in the reminder part of the season.