The last large-format Sears department store in Pennsylvania, at the Willow Grove Park mall in the Philadelphia suburbs, will close its doors permanently, perhaps in about a month. “They’ve been dropping like flies,” said Jack Batra, who is known on social media as “List Man Jack” and part of a loose-knit community tracking through online postings, media announcements, and job boards the demise of the once-expansive Sears retail chain. They estimate that only 16 large-format Sears stores remain after recent announced closings, including a Sears store shuttering in Fort Lauderdale, Fla., on Fri…