I found this on the website: "Additionally, you acknowledge and agree that American Express will verify your Card account number and provide updated Card account information to Priority Pass from time to time. Priority Pass will use this information to fulfill on the Priority Pass Select program and may use this information for marketing related to the program. Once enrolled, Platinum Card members in good standing may access participating Priority Pass Select lounges by presenting your Priority Pass Select card and airline boarding pass."
I assume if you cancel, you are no longer in "good standing". I also would expect Amex to notify Priority Pass of your account cancellation. Thus, leading to cancellation of Priority Pass. Since Priority Pass is a feature of the card, and not something that is directly paid for, your Priority Pass will be cancelled and all you will receive is a prorated Platinum fee.
