Sterling and Sane are both incredible players, they're very different but compliment each other perfectly which is why it's such a disappointment if Sane leaves. If/when Sane leaves, we also lose out on Sterling's ability to score 15-20 goals a year from tap ins at the back post. It's imperative we replace that natural width on the left, even if it's with a different skillset to Sane, the quality of delivery is the most important quality to replace.
Pep's new #2 will hopefully reinvigorate that right/left balance, as he appears to be very focused in creating width and opportunities to provide crosses from the little I have seen and read so far.