Amex may cook up a product to replace the Costco AMEX, but I'm sure Costco will try to find a deal with Visa or MC. I've used the Costco AMEX as my main CC for last 6 years or so. Sad to see it go.

If the warehouses drop AMEX as a payment option and do not replace it with at least one other CC option, I'm curious how it will affect Costco's business. I hate paying for things with debit cards (or worse, cash).