Most likely yes. Can't speak for other organizations but the one I work for licenses RHEL on our critical servers and uses CentOS/Alma on all non-critical infrastructure. Obviously the reason that is done is because it's easy to support what's essentially a single OS. With this new change, if Alma/Rocky go away we'll be looking at either Suse or Ubuntu most likely and RHEL will go away completely to be replaced with the licensed equivalents of Suse or Ubuntu so that we only need to support a single OS.

Not directly but it might cause some upstream vendors and projects to rethink weather they want to recommend Red Hat as preferred platform and if the hosting vendors turn off the Red Hat clones that's going to ripple back to Red Hat, as a lot of corporate linux users will gravitate to the distro that's recommended by the application vendors.

Part of how canonical challenged Red Hat is that they deliberately made it really easy for a developer to run Ubuntu on their workstation and test environments.

No, it won't unless the customer is also using upstream stuff elsewhere. But it will close an avenue of new customer acquisition. Can't say how often, but it happened that someone needed support for an upstream software (which is a big no-no) and ended up buying a downstream license.

No (paying Red Hat customer).

Current customers? Probably not, but it will hamper the flow of future customers for sure.