Well i gues there is still some vendors no matter what faction you choose ...
Unless you do as Swen asked, and literaly betray everyone.
Besides vendors that are temporary ...
Those smugglers named Z*something* cant remember ... alleged paladins of Tyr ...
There is Druid vendor, tiefling vendor, and goblin vendor (there are two btw) ...
They are still there untill you betray related factions ...
And even if you choose to kill them all, for some reason ...
Volo in your camp, if you choose to save him works as another vendor.
And since he is not related to any faction, he will not even turn hostile ... unless you attack him.
And with extremely limited resources, there is ressurecting skeleton.
Also many non-vendor NPC are open for trade, even if they dont have much.
Not sure tho, but i bet you can trade with most ... if not all friendly npcs you met.
