Not my expertise either, but it seems that the advantages of vertical integrations between fabbing and chip design being large was the "common wisdom" in the industry for a long time. But it seems that lately AMD/NVIDIA/TSMC and others have demonstrated that fabless chip companies and merchant foundries is a model capable of producing the highest end chips as well.
And yes, if for some reason Intel would want to fab their chips at some merchant foundry (see my sibling answer to yours why I think that's unlikely, but just for the sake of argument), I'm quite sure they couldn't just email the RTL's to the foundry and get chips back. It would take a lot of work to adapt the chips to the merchant foundry's process.
