Won't matter if Torres is there or not IF Costa can stay fit. He's already playing well and looks like a pretty short world cup has helped him to heal up. From what I've seen in pre-season he doesn't look like he's running slower or in pain. With hamstrings you never know, Messi/Aguero having a hell of a time coming back from hamstring injuries, constantly re-injuring, looking not comfortable when they are playing, less willing to run, not running as fast, not using their explosive acceleration.
Costa looks fairly comfortable, if he has a hamstring constantly going again season Chelsea will struggle without replacing Torres. Fabregas had a similar hamstring injury at Arsenal, struggled and kept being reinjured in his last season and for the first 6 months at Barca.
On that point, I wonder how Barca will be with Messi still looking to be not at ease and playing till late in the cup, not ideal. Aguero for City another big question mark for this season.