Yes, the breakage on the credit has to be very high, so high that it doesn't matter much whether AMEX or Saks is funding it. Say there are 120,000 AMEX Plat holders in California (my best estimate based on 1.3 million total Plat holders) and two remaining Saks 5th Avenue stores. If everyone did the $50GC semi-annual trek, that would mean about 330 people per day per store. That would be pretty extreme and unlikely given that Saks is a long way off for many people.
I think most cardholders are hopefully going to be fairly rational about this. Spending an hour of time and a few gallons of gas to buy a $50 gift card makes little sense. I am currently in Las Vegas, but about 7.5 miles from the Saks store, and I have no “business” in that area. I am not going to spend my time buying a Saks gift card with the hope of being able to use it in January for some overpriced item…