No he won't. Regardless of how many times you say it. If you think City will sell Aguero in the next three weeks I don't think you've been paying attention. That goes for all the other posters who seem to thinks it a viable option.
Plus, we ain't signing Mbappe and Sanchez. I doubt we are getting one of them, never mind both.
You can doubt all you want, but if it did happen then there is no way that Sergio stays. I think that this is pretty much the majority opinion. He'd get very little game time and he's still far too good to sit most of the season on the bench.