No, the fastest path is putting the signature back. But I guess Route53 won't let them do that.
unless you are a customer of a very tiny ISP the odds of getting the person on the phone who has root on their recursive caching nameservers provided to DHCP clients are minuscule.
And chances are they wouldn't flush that entry for you anyway.
They should at least say something like "we're working with major ISPs to resolve the issue". It really comes off as walking away from a disaster of their own making.
I wonder how much electricity will be spent flushing then repopulating the caches of each and every DNS server on the globe. Prolly not that much?
No need to flush the full caches. Clearing caches for individual zones is not uncommon.