You get two types of backroom staff appointments. Some backroom staff stay at the club regardless of what happens to the manager, they are club appointments and might be put on rolling contracts.
Then you have the ones that come and go with the manager (often his assistant and maybe one or two others like for example Koeman had with his brother and fitness coach) and they have the same length of deal as the manager so a club can more easily get rid of them all at once.