That makes no sense. If both parties legitimately agree, then there is nothing that the GDPR can do about it. The issue arises if one party decides that they no longer wish the other party to hold on to their data anymore, and the other party refuses to delete the information and withdraw services. The unacceptable business model for GDPR is providing a service that requires personal data in order to function. Google making search unavailable to those not providing PII would be in breach of the regulation.