Come on VVC. The RN will carry on as normal.....policing the worlds oceans and keeping the sea lanes open for the 95% of UK trade and resources, whilst maintaining CASD. The real question is what will the RAF and a standing Army do? This will be a real problem for them as the appetite for UK based training will diminish (local lobby groups against low-flying, tanks etc) and the question of where do you fly all of the UAVs will not have been answered.
If SDSR really does its business it will design in contingency (for post 2015) whereby we mothball (in Arizona) 4 of the 7 C17s, 50% of FSTA (if we ever get that number), reduce Typhoon numbers (poss by RAFVR flying much reduced hours each year, disband the RAF Regt......ie an RAF of 17-20000. JSF training will largely be conducted from the sea...reduced shore footprint and in US waters (noise lobby) and to employ the 2nd CVF. The Army will reduce to about 85000 (reduced Tanks, Apache sqns etc). The RN and RM will form the UK contingency force (Strike and Amphib) and see an increase in patrol platforms (1500-2000 tons) for counter piracy/counter narcotics/border security.
There again....