Why will the Stormcloak leaders that are now in the Stormcloak camps AFTER you have completed the Civil War Questline will not die??? I chose the Legon and after the Final Quest to win Windhelm was finished and the General told me to finish off the remaining Stormcloak Camps, I go to them and kill all the Stormcloaks but the leaders just won't die... How do you kill them???

The answer is a technical one.

They were never set to be killable post civil war. Probably a developer oversight.

I noticed the same exact thing. There are two possibilities that I can think of: (1) The patch did not fix this particular issue, or (2) The patch did fix the issue, but it is a non-retroactive fix, which means you will only be able to kill them after starting a new game and completing the civil war again. This was not specifically listed as being fixed in the 1.9 patch notes, however, it may fall into the category of a fix that was listed that read: "Fixed problem with quest scripts not shutting down properly". Bethesda's patch fixes are sometimes very vague, so it's hard to determine what exactly a particular listed fix actually addresses.