Depends on how you choose to define resource depletion. If you mean physically less of it, I don't think anyone denies that. If you mean scarcity however, it is a different matter. If the demand for a good is falling faster than its supply, pricee can fall while the resource is being depleted. Thus the resource is becoming both less scarce and less abundant at the same time.
Sustainability is a really tough one, as it all rests on the definition.
At the one extreme, sustainability can mean that we leave the world just as we found it. It is wrong to use any finite resource. At the other extreme, all we have to do is be able to supply the things that people want indefinitely. I don't think there is an easy way to say what is right. I certainly have no disagreement that there is morality involved.