Every club on the planet has experienced the heart-wrenching loss of a key player. The trick to surviving the grief, however, is finding a replacement of equal quality. Rangers did exactly that last summer. The legendary Allan McGregor retired, only to be succeeded by the club’s newly-crowned Player of the Year Jack Butland. The impending departure of long-serving left-back Borna Barisic, meanwhile, should be offset by Ridvan Yilmaz‘s emergence under Philippe Clement. Rangers also have purchase clauses in the contracts of Mohamed Diomande and Oscar Cortes, providing a succession plan should Jo…