Think this is the beginning of the end for Sterling now. Can see him being the kind of player who retires fairly early-ish, like 32 or 33.
I think it depends when his pace starts to wane. He's always had two outstanding attributes; pace and movement off the ball. What's disappointing - although not for me personally as he did the dirty on us - is that the other parts of his game haven't really improved since he was a teenager. His finishing is more miss than hit, his dribbling is basic but effective due to his pace, he hasn't developed any playmaking ability and he doesn't come across as a leader (Chelsea captains are James, Chilwell and Gallagher!!).
He mastered the far post overload under Guardiola and his goal and trophy record during that period are hugely impressive. As others have said though, it's really just a footnote in the story of Guardiola, and Man City fans seem much more likely to speak fondly of David Silva or Aguero.
I think he was right to leave Man City as he said he wanted to prove himself and be in contention for the Ballon d'Or. Without that strong all around game though and with the ensuing chaos at Chelsea he's pretty much a forgotten man now. Even Southgate has moved on.
He doesn't striker me as a player that's going to want to drag his career on when he's no longer at his best (like Ashley Young, for example).