If larger companies can run CentOS in production, they also can run Debian or any other distro without a support contract. They could even use a competing loss leader distro like OpenSuse Leap.
Don't get me wrong - I think it'd be great if Debian became the standard, assuming that meant that companies helped develop Debian and poured resources into it as a commons. That'd be much better than depending on Red Hat to do all the work and then not paying for it.
https://wiki.debian.org/LTS/Funding https://wiki.debian.org/ExternalEntities
And from a company perspective, Red Hat has already done a big swap out from satallite to Foreman / Puppet to really pushing Ansible. Similarly, they've stopped doing oVirt in favor of cloud style OpenStack, nee OpenShift. Which is great if you're building your own cloud fabric, but not really the VMWare / HyperV competitor oVirt was which is something lots of mid size orgs need. ProxMox still seems to be going.
And for people who aren't paying for support - I imagine they have skilled in house teams that can certainly figure out Debian if they've been orchestrating CENTOS and now Alma say.