I don't know, but I do know this: kings are pretty tough. My guess would be that either the foam will be eliminated at some point. I certainly hope so.

Just so you know, I have had kings swallow unintentional objects such as a decent-sized piece of paper towel stuck to a thawed rodent, a piece of bark (way back in the day when I though bark was a good substrate) and once a rubber band. All of the "victims" were fine. The rubber band eater lived in my care for over 18 years.

I suppose it is one of those things whereby if the object does not get lodged in a bad spot, it is not a problem. Hydration is important as well for a healthy digestive system.