I totally agree that Lukas Modric's departure whenever it happens will make a huge difference even with the presence of Tchouameni or Ceballos, either of these players cannot match Modric's brilliance and work rate in the team. If Kevin De Bruyne makes the first leg it will definitely boosts Manchester City's advantage going into the game.
Modric has everything that's needed by real madrid. He is smart, full with experiencem, accuracy on his passing and many more. Ceballos and ameni were not matching to be compared with modric. The gap is very big.
Modric can be considerd as veteran player as well which has more knowledge and experience compared with ameni and ceballos. That's why losing modric was giving great impact to the performance from real madrid.
Sometimes modric was giving long pass with high accuracy that was also helping his teammates to create fast counter attack. Modric has been participating in training before the match against osassuna but i think that if ancelotti keeps him for the match against manchester city which is far more important than against osassuna. It's likely that if modric will able to play against manchester city.
Modric has been agreeing to continue his journey in real madrid. he has been signing a new contract with madrid. It will be last only for another season.