I think Arsenal's CL spot is safe. Chelsea aren't going to win the CL, their win against Barca was a more a product of Barca's attacking arrogance combined with terrible defence. In a more open game, like the one against Bayern will produce, Chelsea would have lost. Barca's hatred of long range shooting, something the likes of Robben and Schweinsteiger are happy to do, make it a far more risky tactic. Bayern are also playing for something huge. With no Terry and a larger forward like Gomez, I think that game as a reference for the next is basically irrelevant, approach will be so different.