I’m very curious as to why he wouldn’t want to stay at DAMS. They were easily the best team in GP2 this year.
However three scenarios come to mind that might explain why he will leave the team:
1) He doesn’t have much say in the matter. He may not have enough money to continue running in what is becoming a very expensive series, or the team may feel that he is not living up to expectations, particularly after Valsecchi won the title and he could only manage tenth (Calado, the highest-placed rookie, was fifth overall).
2) He thinks that joining another team will give him a better chance of making it to Formula 1. In this case, I would expect him to go to Lotus; Esteban Gutierrez has been links to a Sauber seat, whilst James Calado is believed to have run out of money.
3) He is leaving GP2 altogether, probably for Formula Renault 3.5, which is the better series these days. Although DAMS has a team there, Nasr would be better off trying to get into Tech 1, Arden Caterham or Fortec.
I’d say the third scenario is the most likely.