The 'plan' is of course briefed pre-flight. For a trail mission, the pre-flight trail plan would be printed off-aircraft (or on-aircraft if time is tight) for crew review. Any significant in-flight change of plan can be printed on the cockpit printer in flight, so that the pilots do not need to gaze at any specific screen at the time - they can review the agreed plan change at their leisure, should they so wish.
In any case, inter-crew SOPs are such that the AAR mission can continue seamlessly even in the unlikely event of a double hardware failure denying the crew the use of the Mission System.
It would be perfectly possible to add a flight deck repeater display for the Mission System as the video system has ample spare connectivity; however, it simply hasn't proven necessary over the many years that the system has been in operational service.
When do you start your Voyager course, 3engnever?