Close to zero chance of Intel being allowed to buy AMD, unless they open up x86 for others. Although if alternative architectures like ARM start gaining some actual ground on desktops/laptops, say in 20 years, then it might not trigger anti-monopoly bells as hard.

Then there's the option of Intel buying just the Radeon parts of the company. However seeing as the GPU market seems to be growing fast, it would have to be quite the offer for shareholders to agree.