I have experience with 2D (which is why I'm always asking 3D questions because I suck at it) and have used AI before.
fhein is right, the idea of a MMORPG is to interact with other players. Just do a prompt system:
1) Player clicks on Bartender
2) Bartender says: Hello, Welcome to my Pub. What are you looking to do?:
Buy a drink
Nothing, just wanted to talk :)
3) Player clicks on one of the two choices that appear on his screen:
if choice 1) Pull up an inventory menu of the drinks to choose from
if choice 2) Exit the conversation / dialog
Of course it will depend on how you are implementing your game and different interactions, but it's easy if you just limit the options. Players come to the bar for a reason: to buy beer (or something else you might implement). Why have the bartender bullshit you for a while if it's just going to delay your time in getting the beer?
Or you could have some really new uber idea that needs the AI to make your game the ultimate one out there.
Great man, go for it. But also realize that it will take processing time on your server. Everything takes clock cycles. Limiting your AI will not only save you production time, but will speed up the game.