While a common sentiment, I think this concept misses the entire purpose of war. The purpose of any war is to impose your will by force on another, and by extension, prevent your enemy from imposing his. A drone-on-drone war may be an opening salvo, but unless drones are the only means available to an aggressor or defender, they will never be the only means being used in warfare no matter how technologically advanced things become. As long as an enemy has the will and capacity to resist force upon him, or still has the ability to impose his will by force on another, the war will continue. Once enough of one side's drones or robots are sufficiently defeated, it will be people that are the means for imposing or resisting force, so they will eventually always be the ones fighting and dying.

I can't imagine if Ukrainians had incredibly advanced drone/robot tech, them throwing all their drones at the Russians, loosing them all, and then saying 'Well, we used up all our drones, I guess we'll give up now.' It always comes down to removing an enemy's capacity or will to resist force, and people will always be part of that equation.