I personally think this is comparing apples and oranges. The servers are expensive not because they can be used as IC nodes, but because they’re sophisticated hardware capable or generally useful compute. If the IC network crashes, is attacked, or otherwise damaged, those servers would continue to remain expensive pieces of hardware. The same can’t be said for staked ICP (that’s the point of proof-of-stake).
I’m thinking that if the IC is to be a world computer, there shoudn’t need to be a dependency on off-chain systems and structures. If all of those things you mentioned are handled on-chain, then they then become exposed to the attack that they’d be intended to prevent.
A world computer needs a protocol-level solution to these sorts of challenges, for the sake of dependencies and scalability. Proof-of-stake is a highly effective protocol-level incentive alignment mechanism.