Of course Slayer would still be Slayer, even more so cause king and Hanneman are the main songwriters anyway, it would definitely be a crazy turning point for Slayer if Araya left, cause his voice is obviously such an important feature of the band just like Igor's style in Sepultura, but it would still be Slayer and it would still be Sepultura. Put yourself in Kisser's shoes, would you decide you'd rather go back and start your whole career over (or find a new one) just because the other guy decided he didn't want to participate any more? he was also a part of those albums and those songs, why would he give up on them? Millions of bands have much more lineup changes than Sepultura and have no original members but for some reason people love to pick on Sepultura.
Edit: I agree on the comments about Kisser being simply a former roadie being retarded, the guy's a much better rhythm guitar player that Max without a shred of doubt, and he'll probably never match the songwriting of Max's riffs in Sep, but I don't think he's any worse than the latest Soulfly and CavaleraC albums