“Glee” will return to its roots in the upcoming series finale (Friday, March 20, at 8 p.m. ET) when the show flashes back to “2009,” also the title of the episode, and offer a new perspective on how New Directions really came together. In doing so, the series will pay tribute to the late Cory Monteith, whose presence was felt during Friday’s PaleyFest panel, moderated by EW’s own Tim Stack.