The defence was fine without Kiko last year, and it's his second major knee surgery already. With that being said, he was a stud, and he was on a rookie contract, whereas LeSean is older (26) and is also a RB who has a 7M cap hit over the next three years.
If the Bills can get Iupati and more help on the OL, the defence should be just as good as last year (plus Rex) and then I guess this improves the run game. I still am holding out for Bradford, or maybe Matt Moore or Jake Locker. I dunno. Bills need a QB. Ugh.