Petrov can improve his first season didn't go especially well, but considering his back ground (LADA ice racing) he's done extremely well for the little amount of single seater racing he's actually done, I think Petrov is an extremely raw talent.
On the other hand, Heidfeld from a buisness point of view, makes absolute sense, also I'm sure Kubica would be happy knowing an old team mate was driving his car.
With the 3rd drivers they have, it does seem a bit odd that they would consider Heidfeld anyway, it's almost like they didn't really wanna use their 3rd drivers for anything else other than tests anyway, but when you think about it, Senna doesn't know what a decent car feels like yet, Fauzy is just a LOL, and Tung is a big LOL too, but Charouz, other than Senna, I would say should have an opportunity for this.
You can't really argue with Renault though, Heidfeld is a decent driver, in his last races for Sauber he scored as many points as De La Rosa in 5 races and nobody complained that he got a seat did they?