RI
Problem is you would lose access if you left Sky to that copy on the box.
It's like Royston Vasey, you can never leave...at least without losing your access to HD Movies.
Sky have said on multiple occasions they will "look at" sending Blu-Ray disks out but I suspect it could be argued the HD copy that you keep on your box (that you can delete and restore as needs be) serves as your Blu-Ray/HD copy or digital copy, and the DVD is for every other TV.
Problem is you would lose access if you left Sky to that copy on the box.
It's like Royston Vasey, you can never leave...at least without losing your access to HD Movies.