I know this won't be a popular suggestion because of the team he plays for, the style of play and the lack of an exotic name but I think Dwight McNeil could be worth a serious look if and when we have to replace Sane.
He's not got the outright pace of Sane but he's got really good delivery from the left and is naturally left footed which would give us far better balance as a team. I think with Guardiola teaching him when and where to make runs, how to "keep it simple" and his natural work rate and energy, he'd be a very good potential option. Partially due to a lack of naturally left footed left wingers.
The other one I really like the look of is Bukayo Saka at Arsenal, only 18 but he looks very interesting and can play left back as well as left wing.