When people talk of missing something like a possession, an experience or a person in their lives we often think they would like to have it back. This need not be true always.
We can miss something or someone and that can be just a feeling of nostalgia. When people talk of missing their childhood or school life it only means they were looking at their past wistfully and not that they want to be a child again or go back to school.
The same way we can miss people in our lives -people who are both dead and alive. But this need not always translate into wanting them back in our lives though in some cases it could.
We may miss a relationship that we shared with someone. This is looking back at a relationship and thinking that was good while it lasted. The other person may have changed, we may have changed or both may have changed and neither would want the relationship back. So missing a relationship does not have to imply wanting it again the same way.
We may miss a job or work. We are just looking back and thinking that was a good time. But now we could be in something that is different and making a different kind of meaning in our lives and may not want to go back to the old ways at all.
Missing something is a feeling of wistfully looking back at something good in our past but not necessarily wanting it again.