Burnia sends their million autonomous weapons to kill the million people they judge are most crucial to Hevonia's war effort, prioritizing Hevonia's political leadership and military officers.
Hevonia, meanwhile, sends their million autonomous weapons to destroy Burnia's autonomous weapons, when they can find them, but not to attack any humans.
Who wins the war?
I think Burnia does, because even if Hevonia's weapons are 99% effective, Hevonia's government has still lost its top ten thousand people, including all of their military officers, while Burnia has only lost half a billion dollars. That's going to make it impossible for Hevonia to keep fighting. And I think 50% effective is more likely.
However, if that doesn't end up with a radioactive wasteland, we'll probably find out shortly afterwards what happens when every two-bit drug cartel or extortion mafia can cheaply assassinate anyone, anywhere in the world, with an ambush drone.
I wonder what's stopping them right now. They used drones to smuggle drugs already.
What matters, given that it meets the minimal bar of weirdness to be potentially worthwhile, is whether it's correct. Which depends on what future combatants will do once weaponry actually is autonomous, not what Ukraine and Russia are doing with remotely-piloted FPV drones.