I don't know about "not one of those guys would have let Gon die", I don't think they'd have time to react to a death blow. I'm pretty sure Kurapica and Killua would've been able to handle Hanzo. Kurapica has looked quite uber when he has his red eyes thing going, and Killua, well... it's Killua, he looked very unimpressed by Hanzo's performance and we know he's a bit of a monster.