Hi ! I have the same kind of question to ask, but from the opposite point of view (and as it does concern the warlock, I felt I could parasite your topic, if you allow me to).
On the game I've juste started, one of the players is a warlock. He hasn't got the Shatter invocation, but I'm concerned about this eventuality. Because if he does, that means every guy I'll throw at them will see his weapon shattered right from the start. As they're actually level 2, and won't go that much higher (this is kind of an introduction to the game, to let them discover the mechanics and stuff), no magic weapons for the bad guys ...
I could use monsters with natural attacks only, or have any humanoid they encounter have a few spare weapons ... "Well, that barbarian draws another Two-handed axe from his backpack ... Yes, that's the third one, I know ... He's got a big backpack." And not using humanoids is a bit frustrating, especially when they are supposed to be the main villains in my plans. But on the other hand, just saying "ok, he has no weapon left, you get AoO any time he tries to attack" is just going to make encounters a piece of cake for them, and that doesn't seem a good choice either ...
What could I do ?