I never play murder hobos so it’s part of the game I have no experience with.
You dont really need to ...
There is vendor in Zhentarim hideout, that turns hostile quite easily ...
There is vendor in Tollhouse, that turns hostile if you side Karlach ...
There is vendor in Goblin Camp (two of them in fact), that turns hostile if you ... well, actually dont play murderhobbo, and side with Tieflings.

The original complaint was that when characters die loot appears that isn't in their inventory, whereas the change Ragnarok mentions would seem to explain the opposite, ie that loot disappears when characters die.
Both ...
There is Inventory A ... that is what NPC is holding as long as they live.
There is Inventory B ... aka Loot ... that is what NPC is holding when they die.
If you knock NPC out ... it still holds its inventory, therefore you can take that ... if you kill it, its replaced with loot it gets after death.
And yes, it is (or was last time i tryed) possible to take both by knocking them out, loot, then kill them and loot again.So if you sell +1 Greatsword to a Vendor NPC ... it have it in its inventory ...
If you kill the Vendor NPC later ... the sword dissapears.
AND another items it didnt possessed previously appear.
I dont like it at all, it makes no sence.

Yep, the current code procs a treasuretable on death...so maybe larian can change it to death or knockout.
Wich would only lead to de/materializing items on both cases.
I for one would certainly vote for return to previous state, where NPCs just had their inventory wich we could trade/steal/loot ... and thats it.
Also, on slightly unrelated note ... i also believe that if NPC have some quest reward, that reward should be part of its inventory ... unless its specificaly shown that they create the item for us.