I assumed he just had DNS at AWS, but after re-reading I guess he has DNS _and_ domain registrations at AWS, which would be a special kind of stupid. That's something we were advising customers against already back when cloud wasn't a thing yet to enable fast transfers when stuff goes south

(to clarify: DNS+domain at the same service can be OK, as long as you have nothing else there. As soon as you start having other stuff, keep the DNS there, but move the domain registration away. Depending on which domain make sure you have auth keys, access to the admin domain or whatever would enable moving the domain without registrar cooperation. In my hosting days I did my fair share of emergency transfers and infrastructure to help companies get their basics online again after a SNAFU - totally doable to have first mail coming in again within a working day)