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.
As you said he won't be a direct replacement, but often times it is these situations when a superstar gets injured and a youngster or relatively young player gets his chance that things can go quickly into a positive direction. Replacing De Bruyne one to one as a midfielder is like replacing Mbappe or other top players in the offense one to one. It is mostly not possible. But Guardiola will start thinking about alternatives for the future because he knows that the chance for De Bruyne to be injured more often is only becoming bigger from here. That's a problem he has to solve before the big games are around the corner and suddenly De Bruyne is again injured.