Liverpool can survived without Mohammed Salah in the squad, they play together and the absence of Salah will not pose any threat.
But Liverpool relies heavily on Muhammad Salah to win in most of their games just as Manchester city rely heavily on Kevin De-bruyne to win most of their games as well, taking Salah out of the picture, the absence will really be felt in the Liverpool's future games; However, it doesn't mean that they can't survive without him, but they have to learn to win with or without his presence in the team.
I don't think it's true both teams really heavily on both players as mentioned by you above but then in the case of Manchester city it's no doubts how Kevin de bruyne has been of great impact to their performance and progress in the various leagues they play and all through the period of his injuries Manchester city has been doing well regardless which means the reliance on him isn't that heavy.
His return from injury has really helped Manchester city especially with the fact that haland and doku are currently not present too, with Liverpool Salah is a very key player who no doubts helps the team a great extent this will be the first time this season they are going to play in his absent for this long time, but then I'm sure they will sur look for a good alternative in his absence even recently before Salah got injured at the AFCON, Liverpool were able to win a game in his absence and they did performed really welll which could means they don't have that much dependency on him but his presence has got a lot to helping them especially with creativity.