You are right they are not listed anymore, Softbank bought ARM $31 billion.

There might be some ARM customer who selected Intel as a foundry for their ARM design; the question is how much ARM would have to invest on such a customer.

I suppose the worst case would be an expensive R&D initiative (with ARM paying Intel for prototypes) about how to make ARM cores with Intel's 10nm process, with no usable result. Not likely to sink ARM.

Rolling things over in my head. Warning mere speculation.

ARM doesn't sell silicon, they license IP. However might be they're licensing IP blocks. Essentially a tested CPU layout you can more or less paste into a design. Think Lego's.

Look at the two links I provided. And ARM wants to provide IP compatible with 10 nm to compete with TSMC and GF:

https://www.arm.com/products/physical-ip