Is your definition of leaving, actually leaving and deleting the account? or is it “inactive?” It sounds like it’s inactive.
I can see a use case in our site where this would actually work. We are primarily a public health project driven forum. One of our projects recurs each year, generally from February to Mid-May. While we would like to keep the conversations going the rest of the year, that might not be possible for many of the participants in this category. A periodic digest would keep them in the loop and let them know activity is still going on.