@Cyracuz,
I like this question!
Two subjects: Robots and Humans
Object in question: Money (need thereof)
Currently, money is the reward for human work, rather the exchange for services/goods provided, which is then used to buy other goods and services.
What the question presupposes is that if there is no longer any "work" for humans to do, then how will humans acquire the goods and services they need? The question also presupposes that humans are the only ones that use "money". There has to be some exchange for the services/goods robots provide. Whatever that may be, it will constitute as money to them.
Let's look at a basic principle, "if you don't work, you don't eat". Okay, so if humans don't work, then they don't get money to buy food. So then, what happens? We go back to the barter system of old, like someone mentioned. Anything you "trade" for the acquisition of something else, that is legally allowed, becomes, essentially, "legal tender". So, in essence, we will always have "money" in some form or fashion, no matter what.
Robots are not sentient beings with the capability of controlling the world. An increase in technology has, and will continue to destroy the economic, social, and political structures we humans have built. But, because we are designed to do so, we will create a new system with new currency and new rules. Resources will be acquired by newly structured means. Life will go on, in some way.