Even if nuclear weapons were not in the picture, an unmanned strategic or even theatre-level bomber is a silly idea. The payload/range benefits of going unmanned diminish as the total size of the aircraft increases because the weight and volume required to support a given number of pilots/crew is more or less constant regardless of the size of the aircraft. Additionally, the challenges of remote control/situational awareness that all unmanned platforms face are most acute in precisely the environment a bomber is intended to operate, i.e. far from friendly basing/forces and in at least medium and potentially even close proximity to hostile forces including EW/jamming capabilities.