You are making this way harder then it needs to be. As for boss mobs that drop uber gear, you can't have them always drop their weapon, but you want their fight to include the weapon of course. The way to handle this is have broken pieces of their weapon in the loot table that can be used for crafting when he doesn't actually drop his weapon. Simple.
As for non-boss mobs that don't always have their weapon on them, your example was an elite warrior who spawned with out his sword. Ok. If you run in to an elite warrior who does NOT have their sword on them, then that's a pretty stupid warrior OR a warrior caught off guard. Either way, that warrior does not have their weapon, so they can't fight with their weapon. What's the next best thing, they use their fists. They might even perform berserking moves because they are fighting with out a weapon of choice and become desperate.
Ultimately, you see it as a static mob that does one thing the same way everytime. Hence, you believe the elite warrior should fight with a weapon effect no matter if they are carrying a weapon or not.
The way I see it, this mob is more dynamic my way. If you see an elite warrior carrying a weapon, you know he is going to fight with his weapon. If you see an elite warrior with out a weapon, you don't know what he might do. He is upredictable. The fight is dynamic.
From a technical stand point, what we really have here behind the scenes is two different versions of the spawn with the same name. One is a sword wielding elite warrior that fights with traditional sword wielding techniques. The other one is a fist wielding elite warrior that will pull off more monk like moves and could go in to a low defense high offense berserker stance when he gets to low health.