It is very unfortunate that De Bruyne got injured and he is probably absent for a long time. It becomes more complicated because Bernardo Silva got injured too. In this situation, Man City is very possible to make a plan for signing a new player. Lucas Paqueta looks a good player to replace the position left by De Bruyne and Bernardo Silva. Man City needs an experienced AMF, it is not enough to rely on Cole Palmer for the whole season.
I doubt if Man City can sign Khvicha Kvaratskhelia, it won't be easy to sign a top player like him. I am sure Man City may have a bigger chance to sign Florian Wirtz, Julian Brandt, or Lucas Paqueta.
I don't think he is a direct replacement of De Bruyne but I like that Julian Alvarez will start more matches. I think he might just be what Pep needs, and I'm sure that what he lacks for in finesse he will make up for in sheer determination.
Still, like you said if City want a replacement they have plenty of options to choose from.
Napoli will not let Khvicha Kvaratskhelia leave the club that easily and they will try to hold him harder than Victor Osimhen. He is the pearl of the club and even fans of Napoli said many times that they want him to remain with them.
Manchester City will think about a replacement for their stars if their absence will be long enough, otherwise they will figure a temporary solution.