If Pep thought selling Sané would put our season at risk then he'd not be for sale. End of. No one at City would overrule him and he's far too obsessed with winning to just have not weighed everything up.
The fact the club seem willing to sell, albeit for an incredible fee, means Guardiola thinks he's got what he needs or has someone lined up to come in.
Maybe he's seen decided Mahrez is going to hit POTY form, maybe he's seen one of the kids show something, maybe he's decided to change the formation.
I've got no idea what the solution is, but there's no chance he'd sanction a sale that would leave the squad short.