Personally, with that kind of product, a few days at the most...as long as it's well wrapped in tinfiol to keep fresh. Don't use cling film as this just tastes the pate. - The problem lies in if you take it from the fridge and serve it properly at room temperature, then it'll shorten the life majorly...
Best advice...Buy really good pate and you'll eat it so quickly, it won't be an issue! :)