Hm! Complex.
Can be made easier though. A gamey workaround is to place all of the weapons into an ammo crate, and then blow that one up, since that you can do no problems. I wouldn't recommend going into any firednears or whatever, that might be terribly complex - especially as it's a little uncertain as to how exactly the weaponholders that are created when an AI places a weapon on the ground work (as opposed to the ones you create yourself).
It all depends on the scenario, really. Is the AI carrying the launchers, and you're forcing them to drop them and then destroying them? Or are you sneaking in and destroying them before they're even picked up? The second one is pretty easy: just make sure the launchers are inside an ammo crate instead of laying about, and boom. The first one you could solve for instance by having a super-short blackout, during which the player "disables" all the launchers one way or another (just removemagazine the launcher ammo, for instance) - or heck, even do it as an action attached to each AI that just removes their magazine. If you can do it with dropped weaponholders too, go right ahead.
Since yes, destroying weaponholders doesn't seem to actually work
Thus -> workaround time!
Depends on the scenario, as mentioned.
Wolfrug out.