Lol.... Have you even played Warcraft 3? Mannoroth's character is too arrogant and prideful to ever even entertain the thought that someone would kill him, and why should he? He has dominated countless worlds and species and left virtually unopposed until his assimilation into the burning leigion, and even then he just grows stronger.
And to have a kilswitch like that for an orc? After what Mannoroth thinks of them? No way. Seriously, go read his wowwiki or something so you can have some kind of idea about what argument you're trying to make here.