If Sergio will stay for another 3 seasons, which I hope he will do. Come on Pep get the club to offer Sergio another 3yr deal on top of this last year of his contract. Maybe by then he will be come the overall top scorer in the premier league. Sergio scoring 20 goals a season over the next 4 seasons would put him close to if not surpass Allan Shearer's record. With Sergio already level with Frank Lampard, and only 10 goals behind Andy Cole, there is no reason why he cannot finish ahead of Frank by the end of the season.
So in what will be Sergio's last season next season, he should be able to finish ahead of Wayne Rooney and go into 2nd place in the all time scorers chart. That is if Sergio can stay clear of injuries.