Everyone is different, as far as what they want to do after an intended placement doesn't go through. Some keep pumping like they were, some reduce the amount of pumping, and some find that it becomes too painful and stop completely. It also sometimes depends on what the likelihood is of there being another possible situation, soon. Anyone who has been pumping quite a bit of milk and wants to stop, or reduce the amount, should do so gradually. Domperidone should be reduced gradually, too. A lady I met on another site was pumping 20 ounces a day, when the intended birth mother decided to keep the baby. She chose to gradually stop everything, and just keep the milk she had frozen.
I think that is one of those things that it is hard to predict exactly how you might feel about it until you are actually faced with it. Although you certainly hope you won't ever have to find out, it is probably good to consider it. It happens to quite a few of us who try to adopt very many times. I had to give back a baby I'd had for 24 hours, once, but I also got six babies that I got to keep!
Best Wishes,
Darillyn