This one still going?
It is effectively impossible to estimate what the UK would have achieved under different circumstances from real world history as is. No one can really say whether it would justify the increased costs of maintaining a EoS presence. Nor is it so simple to say EoS simply stopped after 1966, and might be arguable that it really ended with the Beira patrol, and symbolicaly ended with the handover of Hongkong. Certainly EoS may have formaly ended, but it did'nt end entirely in practice.
Quantify the effect of something that did'nt happen? Unless you believe that the future is preordained then its impossible to say and if you do then its impossible because its all preordained and could not change.
A slip of a surgeons scalpe has its consequences for Eden and his decision making, ending in war, and humiliation for the UK, and onward to revolution in Yemen and the events in Aden. Beyond that its not clear what the effect was, let alone what might have changed.
What happens if the surgeon does'nt make that mistake?
An Austrial corperal has a bad dream and gets out of his bed for a walk, seconds later his bed and fellow men are destroyed by an incomming shell, young Schuklgruber believes he's been marked for destiny. What happens if he does'nt get out of bed?
There is no simple in this because for things to be different, they must be different and over a wide spectrum and history, possibly back to Suez, possibly back further.
A host of decisions made, across government created the situation that lead to the '66 decision.
A prescence could have been maintained in a more formal sense than was after then, had things been different, but that difference needs to start much earlier.