I think Granada will definitely be relegated next season. If Madrid don't beat them then another team will beat them. Moreover, you could see that that night Real Madrid only fielded their second tier players. They have won the league and will play in the champions league final. There is no benefit for them in fielding their core players. Actually, Real Madrid is not motivated to win because they really don't think about this match. But this result shows that Real Madrid really has that player and a good second tier player.
They have been relegated, the points they can still get are 9 points, while their distance from the team in a safe position is 13 points, so it is no longer possible for them to catch up with that distance. They have to enjoy the last 3 matches in La Liga this season, because next season they will no longer be here.
Cadiz still have a chance to survive the relegation zone, but it is also very difficult for them to get it. Because apart from having to wipe out the remaining matches with a win, they also have to see Celta Vigo lose at least the 2 matches they play.
Ancelotti can carry out the player rotation plan safely after Real Madrid secured the La Liga title this season from two of competitor Girona and Barcelona. Ancelotti will certainly provide more opportunities for his second tier players who have been on the bench, of course this can help them gain better self-confidence after being neglected throughout the season.
Rotating players will be carried out by every coach who has secured a title, this can provide sufficient rest time for the main players who are tired due to the busy match schedule and intense competition. Main players are certainly needed in all matches, but Ancelotti will not force them to play as long as the second tier players can produce satisfactory results.
They have good squad depth, so when they rotate, their game is not much different from their game when they field the main squad and interestingly these players are young players who can carry out their duties very well if they are given the opportunity to play.
Real Madrid has a bright future with the players they currently have. Ancelotti has indeed played a role in building this, because what he is currently doing is going very well, and their transition from senior players to young players also looks very good, their transition does not show big gaps which means they are very successful in doing it.
The regeneration they have carried out so far has produced good results, although I don't think this is the actual fruit, because I think there are bigger fruits in the future that they can reap.