Retiring the Hercs at any time sounds patently stupid to me but then what do I know.
I would suggest the RAF and British Mod make a final decision of wether or not the UK is to have a strategic/tactical Air Force with the ability to project power outside the Western European region or not.
The C-130 is a very reliable and proven aircraft with an existing logistical trail in place....with tremendous ability to accomplish whatever task is thrown its way.
The real selling point is old fashioned interoperability with literally dozens of Air Forces that use the same aircraft.....how many will have the A-400?