Bruno Senna and Sebastičn Buemi are the only one expected to get a race drive (though not sure).
For what concerns Honda, Button is almost safe, while Barrichello seems to bid farewell to F1. Lucas di Grassi and Bruno Senna are the possible substitutes for Rubens; I think Bruno has a better chance, as he's got great sponsor and in my opinion is faster, though less experienced.
Then Toro Rosso has yet to confirm their full line-up; I expect Seb Bourdais to retain his seat (he deserves it, at least!), and Seb Buemi to be promoted from Red Bull Test Drive to Toro Rosso Race Seat.
There's still a possibility for Takuma Sato (but I wouldn't like him, as he's less skilled than the two Sebs in my opinion) and even Senna (if Honda doesn't take him) and Barrichello have a chance.
So in my opinion:
Sato and Barrichello -> out of F1
Di Grassi -> still Renault test driver, with Grosjean
Buemi and Bourdais -> Toro Rosso Race Drivers
Senna -> Honda Race Driver, with Button
(Jaime Algersuari [predictably] -> Red Bull Racing Test Driver, with occasional tests for David Coulthard)