A 42-year-old man with a 10-year history of alcohol abuse presents to the emergency department with severe epigastric pain radiating to the back, persistent vomiting, and fever (38.5°C). On examination, he is hypotensive (BP 88/54), tachycardic (HR 118/min), and has marked epigastric tenderness with guarding. Serum amylase is 1240 U/L, lipase 2840 U/L, and WBC 16,200/μL. Contrast-enhanced CT abdomen shows pancreatic necrosis involving 40% of the pancreatic parenchyma with peripancreatic fluid collection and no gas. His APACHE II score is 11 and SOFA score is 3. Despite aggressive fluid resuscitation, antibiotics, and organ support for 72 hours, he remains febrile with worsening clinical status. What is the most appropriate next step in management?