Projected cost of persistent storage is still tricky. But, yeah, something along the lines of "Turn off ongoing activity and you have to true up persistent storage soon or it goes away." I don't think one would actually implement a system where a circuit breaker immediately and irrevocably deletes all persistent storage.
And, as you say, it makes sense to have a pool--whether it's your whole AWS account or not--where you can turn on the "burn it all down" option if you want to.
And, as you say, it makes sense to have a pool--whether it's your whole AWS account or not--where you can turn on the "burn it all down" option if you want to.