A baseball season had just ended at Fenway Park on Monday night, but the fans who packed the seats turned their attention to making sure they got one more glimpse of the slugger who had thrilled them since his arrival in 2003. They would not be denied. For nearly 10 minutes, their roars shifted from “Pa-pi! Pa-pi” to “Thank you, Pa-pi!” and then, “We’re not leaving.” Made aware of the situation by the PR staff, David Ortiz lit up the Fenway faithful one last time by coming up through the dugout steps and back out to the field.