I agree that support can end more abruptly with open source than with Microsoft.
But judging by the lack of complaints (or even interest) in this forum about the Centos move-to-Red-Hat news that I posted . . .
Support may not really be much of an issue for offices who simply run Centos to host AC as a virtual machine.
While Microsoft may not exactly have left customers hanging, offices still had to pay to upgrade from Server 2008 to 2012 to 2016 and now to 2020.
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In any case, Microsoft upgrade installations are far from a trivial process in themselves.
In contrast to installing any version of Microsoft Server, Indy once wrote:
"I can (and have) talked a client on the phone through a CentOS install in less than 30 minutes, they can take ANY computer with the minimal specs, install CentOS, and then launch their VM, or a copy without having to depend on AC to be available to activate the database so they can get into their own data."
https://acusersforum.com/ub/ubbthreads.php/topics/71705/re-ac-amazing-backup-service#Post71705***
That was about ten years ago, but I haven't seen anything about Centos installs just for running virtual machines getting harder.
And Centos users who want support can move to another Linux (such as the Red Hat that's replacing it), just as Microsoft Server 2008 users end up moving to later versions.