The cost of catastrophic situations is still ultimately too high in the US without or with insurance.
Instead of annual out-of-pocket maximums that are mandatory under the ACA and make that unlikely, plans used to have kind of the reverse: lifetime coverage caps that particularly severe conditions could exceed. (This is one of the reasons premiums are higher for superficially similar—e.g., what services are covered and at what cost sharing rule befoee reaching caps—coverage under the ACA.)
I can't see how it can happen post-ACA, unless the condition as a practical matter requires services that are entirely outside the scope of coverage.