How do you explain that comment he made that he'd like Gon to survive if possible? That's an internal monologue, so he doesn't need to lie. If he just stopped helping Illumi, then Gon's survival seems to be 100% possible. Then there's that image where Gon's merely one of Hisoka's many playthings. Gon's a particularly promising one, but the very reason Hisoka doesn't even bother fighting Illumi shows that having Illumi has a role that makes him more important than the mere enjoyment the others provide.