copy of TOS:
"19.15 Risk of Rapid Adoption and Insufficiency of Computational Application Processing Power on the Ethereum Network
If the Ethereum Platform is rapidly adopted, the demand for transaction processing and distributed application computations could rise dramatically and at a pace that exceeds the rate with which ETH miners can bring online additional mining power. Under such a scenario, the entire Ethereum Platform could become destabilized, due to the increased cost of running distributed applications. In turn, this could dampen interest in the Ethereum Project and ETH.
Insufficiency of computational resources and an associated rise in the price of ETH could result in businesses being unable to acquire scarce computational resources to run their distributed applications. This would represent revenue losses to businesses or worst case, cause businesses to cease operations because such operations have become uneconomical due to distortions in the crypto-economy."
This is not saying if 1 ether gets too expensive it fails; it is saying that if adoption rises too fast in comparison to growth in mining it could fail. A high price encourages mining, so would actually help. If the price rises, then that doesn't mean that apps and services using either will find it too expensive, because as long as mining keeps up with the price rise these services will just end up paying a smaller fraction of an ether for the resources they are using.