So Julie said that they offered Chris a regular role but he preferred that Kai not be redeemed.
I don't know how a 'I'm going to destroy you all' would have worked though. Unlike the previous villains who had a motive for sticking around what would Kai do? To want power you have to at least care a bit about others and Kai didn't before the merge. Klaus for instance wants people to love/admire him. And there's only so much he could screw around with the main characters before they'd have to get rid of him. Plus he wouldn't have been able to really screw with them because the writers are protective with the main characters.