A 'factor' in future worldwide conflict concerns our responsibilities to former 'empire' countries regardless of whether they remain Commonwealth countries. For example, a by-product of Jamaican independance is/was that we would 'protect' them for +50 years post independence. Hence the WIGS ship and an anual military exchange program (Ex Red Stripe) in which SME for a multitude of trades and an Infantry Regt would be deployed in a tree hugging exercise. That responsibility ends in 2012 and I am sure that other such former colonies pretty much got independence at the same time, therefore a 'burden' is removed within 2 years.
Of course the Falklands falls within this same bracket and is setting a precident by continued 'occupation' by HM Forces. Mixed signals on the global playing service results. For sure, if the will for the Malvinas raises its head again, the islanders had better start learning Spanish.
Probably not in my lifetime: But I forsee a UK Defence Force as a realistic proposition with a Joint HQ forced upon all military personel. The key word there is 'defence' not 'world stage', and all it requires is a change of mindset from 'empire' to 'small insignificant country' driven by the economy; traditions having been set aside.