They have no choice other than get a new player that can replace him. It doesn't mean manchester city needs to get someone who will be replicating de bruyne. The club is currently seeking a player who can perform at a close distance to him, and finding someone who meets that standard would be satisfactory. I recall that there have been discussions about Dani Olmo being a potential candidate to succeed De Bruyne, however, it is important to mention that Pep's latest statement hinted at his willingness to see De Bruyne retire at Manchester City.