Bosingwa was instrumental in stopping Messi, not once, but twice! Kalou gave us a vital goal against Benfica in that away game from last season CL. And still people celebrate their departure. So I don't see much difference between what you just said for Mikel and other past players. If people want to celebrate, let them. Just as long as they are not abusing a player...and when I mean abusing, I mean like racist slur like with Benayoun.