I don't think the concern is that FB will die, but that FB is in control of the platform.
Outside of any agreement Zynga and FB have, if FB takes an action that hurts Zynga (for example, hiding all Zynga games), there's little recourse for them. Technically, you can still play farmville on farmville.com, but many, many people play farmville by searching for "facebook" in their address bar.
Outside of any agreement Zynga and FB have, if FB takes an action that hurts Zynga (for example, hiding all Zynga games), there's little recourse for them. Technically, you can still play farmville on farmville.com, but many, many people play farmville by searching for "facebook" in their address bar.