The Falls Church City Council is working up a strategy to find a replacement for retiring City Attorney Roy Thorpe, who will be leaving his post as the longest-tenured leading city official next June. Thorpe came to Falls Church in June 1996 and became the chief stabilizing force at City Hall through a succession of six city managers and interim city managers and five mayors. Thorpe quietly notified the Council of his plans to leave last summer, suggesting a process for securing his successor prior to his departure.