Can SDLP coax back its missing voters?

Chris Thornton has put his finger on an important factor, that’s not yet had much coverage. What’s happened to the SDLP’s missing voters? It’s general accepted that there’s a large chunk of Nationalist voters who stopped voting for them, but haven’t gone over to Sinn Fein. Have they joined the Unionist middle class and, as Mark Langhammer memorably once put it, gone off to play golf instead? Or will ghost of the Northern Bank robbery and the McCartney pursuade them to give their old party of choice a punt, if only for one last time?