So how does this work exactly? Well I'm glad you asked... or I asked... or whatever, so let's take a theoretical look. There are two distinct behavioral patterns with all NPCs: passive and aggressive. The passive, or neutral behavior is obviously used when the NPC doesn't perceive a local danger, or is scripted; conversely the aggressive behavior occurs when the NPC becomes cautious to a perceived danger, or is scripted. The Savage Deathclaw in the Museum of Witchcraft appears to have its passive/aggressive behavior scripted to trigger between floors rather than between detecting threats (as soon as you come upstairs and walk/sneak out from the stairwell it changes its patrol patterns). What this means is that you can go from fighting it to listening to it walk passively from room-to-room in the space of 2 seconds by simply falling through the floorboards. I can only imagine Bethesda did this to set the museum's ambiance from the moment you enter through the cellar door as the heavy creaks/thumps from the monster above makes for a suspenseful environment. Normally there would be nothing wrong with this if the room were somehow sealed and you couldn't get back downstairs, or if its passive behavior were overwritten once the aggressive behavior was triggered, but in this instance it transforms a lion into a lamb. A big, loud, ugly lamb, but a lamb nonetheless. But hey, if the developers left it in the game then go for it. Let your follower fight as your proxy and save the ammo/aids.
I have to say I'm intrigued to know whether the developer made this a special circumstance, or used a cookie cutter formula that other scripted NPCs are made from. Shouldn't be too difficult to find out - if it doesn't get patched then it's a good bet either they don't know about it, or it's a complex behavioral flaw shared among other NPCs...
