I think Schumi will want to do some racing at Mercedes next year. The car will suit him better, he will know the tyres as well as anyone (characteristics he knows from this year, but new rubber from Pirelli!) and he might stay connected with the team for quite some years still. Mercedes would be stupid to pass upon that opportunity for car sales.
I think Mallya has already stated he is satisfied with both his drivers, so FI only if Sutil moves on to Renault to replace Petrov (Kubica will probably stay for 1 or 2 years depending on their development), but in that case DiResta is more likely.
Renault will want to keep Petrov after his learning year, even though the management now expect him to start getting points in to help them beat Mercedes. If he does not offer enough for them they might get Sutil, Glock, give Heikki a second chance or get someone like the STR drivers or take a chance with their “test drivers” now in GP2.
The new teams are no go. Virgin and HRT will want him to bring money instead of earning a salary, maybe getting a bonus for points earned. And Gascoyne is a real fan of Trulli, and Trulli will want to have something to show for his stint at Lotus before quitting. Heikki is sure to stay, only if Renault would be interested he might jump ship.
If Petrov does get dropped by Renault, i think he would be pretty interesting material for Sauber (with Pedro moving on to a testing role) or he might be of interest to FI and possibly Virgin if they need replacing a driver. His Russian connections might be interesting from a sponsorship view, but the same is true for Renault that seems to be very much into that market.
So no real opening for Nick, maybe if Merc get back into sportscars he would be a first pick or have a seat in DTM.