FCS has the auto-delete function that will delete the dead accounts based on the threshold of how many times the accounts are failing to post.
You can find the function on the dashboard https://www.screencast.com/t/y5Ul1OVxK
Using the dropdown you can setup the number of times the accounts can fail posting before they are considered dead and need to be removed.
There are 2 other ways to run and delete dead accounts but they are not that accurate like this function.
Run the dead account check from the project drop down menu https://www.screencast.com/t/jJEF5D2nEzbp
Run the dead account check from the networks drop down menu https://www.screencast.com/t/d6AH9p6hmm