On current form Evra starts. As mentioned above, we'll see what SAF does during the Celtic game. Heinze is still a few games away from his best. If he was playing well he'd start regardless of Evra's form.
I know we're worrying about defending against Chelski. But we've been defending fairly well so far without Gabby. Chelski's wide threats aren't tall (Robben, Cole, Phillips) and Shevchenko isn't tall either. Drogba will have Rio and Vidic to cover him.
I think Evra's pace will be an asset against those wide players anyway. Moreover, Evra has been very instrumental in our attacks and I assume playing at home against Chelski, we intend to go for a win. If things get rough for Evra during the game then I'm sure SAF knows that FIFA rules allow for 3 substitutions during the game.