To answer the question posed in your last paragraph birdie, it's a moot point I'm afraid. Yours is a completely hypothetical question.
What is not in question is the forensic evidence against Huntley and Whiting. Furthermore, there were witnesses who placed them either at the scene in each respective case or at the scene (in Huntley's case) of where the bodies were found.
As for deterrent's, invariably in such cases these types of individuals cannot be deterred. Deterrents in this type of crime are nigh on impossible. They are predatory criminals who prey on the weakest and most vulnerable members of our society - children.
So, as their guilt is not in doubt and they can never be rehabilitated into society, why allow them to live? Even the father of one of Huntley's victims felt he would have had closure or at least some sense of justice if Huntley was executed. I can't begin to imagine what private hell the parents of Holly, Jessica and Sarra must have gone through, playing over in their minds their respective children's last minutes and the torment, pain and torture they suffered.
As I've stated, financial considerations now creep into every facet of society. Cancer patients are denied certain drugs that may prolong their lives as a result of budgets and cutbacks. Ergo, so it should prevail in the Criminal Jusctice system.