Short term: Amazon pays licensing fees to RedHat to keep the product going, if necessary. I don't know if they're at that stage yet, and big companies can have whatever arrangements they would like between them behind the curtains.
Long term: Amazon develops a new Distro unbeholden to RedHat/IBM. Only a matter of time.
No, they just buy Canonical.
Switching from an RPM distro to a Debian derivative is a much bigger jump than building from RH sources directly.