Their sacrifice is opportunity cost. Which is what TFA describes as the necessary ingredient for a consensus protocol.

> Practical impossibility can be reframed in terms of "opportunity cost": there are limited physical resources and those should have been largely allocated to X than to Y so we can see that X sucked in all resources from any alternatives.

There are a limited number of coins that can be staked at any time.

You fundamentally misunderstand PoS. There is no social trust involved. It will work entirely through economic incentivization, including 'group penalization' when enough validators are offline/byzantine at the same time in the case of Casper. Read more here and try to fully understand this document before you make blanket statements like 'PoS won't work': https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQ

You lose ethers if you misbehave or stop supporting the network. Amount lost depends on what you did and whether your fault was correlated with faults of other validators.