I do suspect that there is a set of circuit breaker actions that could mitigate runaway bills mostly non-destructively. Stop writes to stateful storage. Stop all inbound/outbound data transfers. Terminate EC2 instances (which as you say wold delete data but that would generally be ephemeral data anyway). Halt tasks like EMR.

On the other hand, based on near-universal industry practice, there doesn't seem to be a huge demand for this. I suspect it may be better for everyone concerned to have heavy-duty users control their costs in various ways and for Amazon to refund money when things go haywire without bringing someone's service down.