The colliquial "x86 License" is the AMD-Intel Patent cross-licensing agreement. i.e. All patents related to x86 or any extensions of the ISA are automatically cross-licensed between the companies. While in the past the ISA patent story mostly was leaning in Intel's favor, since AMD64/x86_64 really took off, ISA innovation really became a delicate stack of cards interwoven between Intel and AMD.
So if Intel sells, everyone is fucked until whoever buys can renegotiate the terms of the agreement. And if that's Nvidia, they could just sit dead on the IP and starve AMD of the bulk of their CPU revenue (which is what is keeping the company solvent). And requiring they keep the agreement they currently have would mean requiring AMD to give Nvidia a pretty detailed look at the AMD secret sauce which would increasingly push AMD into the red until they become insolvent, again leading to a Nvidia monopoly.
The US government as well as the EU will not allow that to happen so however things slice, ownership of the x86 ISA patents would not be going to Nvidia.
So for the 2009 cross licensing agreement, change of control terminates the cross licensing for both parties[0]. Since there are far more Intel x86 patents in the last 20 years than AMD, sounds like AMD would be the one more at risk, which I think agrees with what you say. In practice, any anti-trust review if Nvidia is the buyer would prevent Nvidia from using it to harm AMD's business.
