There is more proof of his death in tPoD. "Only nine people living even remembered the game."(p.43) Moridin is talking about sha'rah, a very complex game of stones. Since only nine people remember the game there is no room for Sammael. Nine people living are Moridin(Ishy), Lanfear(Cyndane), Mogedhien, Semirhage, Agnior(Aran'gar), Balthamel(Osan'gar),Messana, Demandred and Granedal. Asmodean cannot be alive because he died the final death(balefire or will not be resurrected), neither can Be'lal, Rahvin or Sammael(either got balefired or is not resurrected yet). And there is more proof of Sammaels death even Cyndane asks Granedal if she knew Sammael was death.