Indeed City played a great game but they need De Bruyne back as quick as they can if they want to go back 2 back UCL champions. This season is way hard for them to conquer the trophy and from my point of view , I do think Bayern are the 1st favorites and then City and Real but you are right , De Bruyne presence will be felt as soon as he steps on the pitch and City also needs him for EPL fight. 
Manchester City really need his presence in the squad to help improve their attack. The Cityzen had lost their best momentum since losing De Bruyne, they had slipped several times in the EPL which made them lose the top of the standings. Manchester City still has a big chance to win the UCL trophy in a row, they must be able to return to their best playing form like last season to compete with Bayern Munich and Real Madrid who appear consistently in different competitions. De Bruyne's presence will create a different atmosphere in the squad, he is expected to make a contribution that can improve the quality of Manchester City's game.I'm sure Manchester City's target is to win back the title in the Chmpions League this season, but the problem is that their strength seems to have been understood by some clubs and they will certainly be better able to anticipate what Manchester City can do this season. They also look declining, especially after losing players who have been their mainstay in every match.