I am not too worried about Linux specifically. RH is a large committer, but a lot of those commits are down to a handful to very talented individuals. One of the other BigCos will sweep them up if RH culture falls apart, imo likely Qualcomm (see their large open source push recently), maybe Linaro (although I dont know much about them).
I think this approach of integration is the mistake in IBM's strategy -- they are squeezing some very slippery customer hard, and IMO this was Broadcom's mistake. The integration must go very deep, be multi-threaded, beyond a single app, OS, whatever, and it has to be a slow noose, not a hard jerk.
If I am IBM, I continue to invest in core, open source, deploy my army of PS people to build custom business solutions around that core open-source (but tailored to their specific issue), use "AI" and very strong core product engineering to reduce risk/time-to-effect, and keep pushing their entire ecosystem (rhel, hashicorp, confluence, whatever else) to customers.
Integrate deeply, then put those annual increases at 9% and build a very healthy, strong moat on a premium brand, experience and level of trust. Better to not give anyone a critical event to justify walking away from you.