An analogy would be to look at US / UK responses to a hypothetical violent confrontation and over-throw of the West German goverment during the tail-end of the Cold War. I'm pretty sure that forces would have been deployed to ensure that security of the bases and the safety of the families was preserved.
That is one point of view - but would the Americans order the German military to surrender and turn over its equipment - including the big ticket items like the Air Force and Navy? Would it deny that any of the forces were actually American? Would is claim that Americans were being attacked, even if it was obvious that none were? Would it claim there were hundreds of thousands of refugees where there were none?
I could see that in your scenario the US and UK might deploy around their own bases. I doubt very much that they would attempt to occupy the German bases.
Indeed, you can't divorce the events that took place from the act of the invasion, but it isn't just that simple to just say that because all of these terrible things took place, therefore the invasion was unwise and immoral. It's more like stock Obama "History will judge the original decision to go into Iraq."