From what I understand, Petrov is on a very short leash at renault, enough that according to my semi-inside source, if he makes a pigs ear of things early on, then Jérôme d'Ambrosio is likely to jump from Virgin to replace him (apparantly 'Custard' as he is known, has been on the renault radar for a while now).
I think Petrov has a new 2 year contract because of the money he brought in, though not sure if that is confirmed.