NPC Despawn?

[Shallith]

I've used a combination of free auto-clicker softwere "Key Presser" and "Free Mouse Auto Clicker 3.7" and in-game macros to check an NPC for an item to respawn in their vendor window
I check back and see the NPC has entirely disappeared. This shouldn't be possible, as it wasn't a killable NPC, not Alliance, Horde, or some faction that can be declared war on, so it dying isn't an option.
I, of course, fear the worst. That some GM have noticed me and temp-despawned the NPC to test what I'd do or whatever, but I've also wondered if there's some kind of system in place that despawns an NPC if they are clicked too fast, too often.
Has anybody else experience something similar?