Here's the thing. I think a lot of us think that Sané is unpredictable in a way that nobody else in that front line is. He can be having an average to downright poor match, and then do something absolutely astonishing which probably nobody else could have done. It can lead to a goal scoring chance, or simply a goal (to an extent this is, and always has been, true of Kun as well, although Kun has developed admirably over the last two seasons).
His unpredictability, from Pep's point of view, is his weakness. But it's ambivalent — it's also his strength. Work rate, that kind of thing, that can be instilled in him at the age he's at (incidentally, most matches that he was brought on late this season, I saw him haring back down his line to harry and/or tackle the opposition, so the idea that he is just ‘lazy’ doesn't wash with me). But what he can do cannot be instilled, cannot be learnt. If he goes, he goes. City will go on, we'll win trophies and we'll have great players. But make no mistake, Leroy's departure will the loss of an x-factor in that attack that, on its day, is incredibly exciting to watch.