According to Entertainment Weekly 2 stars will die in the final episodes of Smallville season 8. This seems almost inevitable as it enters its 9th season and though I like the cast I think this is welcome news.
The story goes on to say that it will be 1 veteran of the show and one not so much.
The odds on favorite for death of someone who has been on the show a long time appears to be Chloe Sullivan with Martha Kent a distant second. With Martha Kent really not on the show any longer this seems a bit of a stretch and it might as well be Lex if that is the case, but rumors are that he may actually be coming back as a character though the actor doesn't really want to shave his head again.
the other character is likely Davis or Tess but again it is only a guess.
Most importantly though, the shows producers insist that these are real deaths and the characters won't stick around.