I personally don't think that's the case at all. If both Sane and Gundogan stay, and we sign Rodri, I think we have a serious problem keeping everyone in our squad happy.
If Sane goes, shift Bernardo to be first and foremost a winger - it's where Pep seemingly prefers him, and he was absolutely excellent there last season. We can still use him as cover in CM if we need to.
Would essentially leave us with:
Central Midfield - KDB, Gundogan, Silva, Foden as the primary CM's, with Bernardo rotating in when required. Zinchenko becomes an option if required and, assuming we sign Rodri, Fernandinho also has the ability to play further up. Give someone like Zinchenko the opportunity to show his ability in his actual position, so when Silva leaves, we have another player ready to enter the fold for depth, rather than going out and spunking £40m on someone to play a rotation role.
Wingers - Sterling, Bernardo and Mahrez as our primary options. More responsibility placed on Mahrez could be what he needs to finally look like the £60m POTY we bought. Not to mention that Jesus is capable of playing out wide if necessary and also Angelino and Cancelo, assuming we sign both, are more than capable of playing in more advance roles. Pep's even played the former in an attacking midfield role before we shipped him off on loan. Signing these two also allows us to play in a back 3 formation with genuine attacking wingbacks, which negates the need of having 4 wingers in the squad.
I obviously don't want to lose such a talent as Sane and it will be a blow, because I think he'll be one of the worlds best in a 2-3 seasons, but I think it actually will solve a lot of problems with players being unhappy with lack of game time, not to mention a significant fee.