From a regulatory perspective, the MOST important thing for the healthcare organization to determine when outsourcing its patient information processing to a third-party Software as a Service (SaaS) provider is the incident escalation procedures. This is because incident escalation procedures define how security incidents involving patient information are reported, communicated, escalated, and resolved between the healthcare organization and the SaaS provider. This is essential for complying with regulatory requirements such as HIPAA, which mandate timely notification and response to breaches of protected health information. The other options are not as important as incident escalation procedures from a regulatory perspective, because they either relate to technical aspects that may not affect compliance (A, B), or operational aspects that may not affect patient information security (D).