In most instances dealing a killing blow doesn't give you an extra turn. And not all teams can do both at the same time.
You can deny Death mana, either by taking it all or draining him. But there is no way to get around not killing a troop. And I suspect it will suffer from the same problem as the dragon soul and inferno king, in that traits are reset upon death and triggered. So stunning it would not work.
Killing hero last, or gaining an extra turn while killing him AND casting a team cleanse is the only way I can see to not let RNG decide who wins.