In reply to ROSP:
Seems a little overcomplicated as described. Once you reach the casualty you can hopefully abseil direct from there rather than having to prussic up, down and then back up the rope.
1. 'Phone for help if possible
2. If there is a ledge or obvious potential belay / anchor point below the casualty possibly lower them to that height.
3. Tie off lead ropes and escape system, possible anchor back up
4. Climb to casualty using Prussic as a safety back up ( spare rope could be used, in conjunction with a device such as a ropeman set up for an upward pull, to use as a 'lead' rope for some of the distance to the casualty )
5. Make casualty safer and as comfortable as possible, setting up a new belay / anchor at their location.
6. Apply any relevant first aid
7. If casualty dead then abseil off and report
6. If casualty alive then two options: Either leave them as safe and warm as possible, with a note explaining, and abseil to get help. (Assuming help / 'phone signal is not far away and it is relatively safe for you to get there). Or abseil with casualty to a better position / base of route.
Many other factors come into play such as nature of injury, level of consciousness, route conditions such as serac or rockfall zones, nature of route such as traverses and availability of anchors, weather forecast, time of day, proximity to other climbers / assistance or hut, 'phone signal, what equipment you have with you etc.