In my testing nodes have been inactive for an hour or more and not removed from this page or the DynamicClusterPeers parameter.
It is intentional to show on the cluster-admin page inactive cluster nodes to show their state, the last contact, etc. If these nodes would be deleted from the admin page, the administration would be much harder.
It would be possible to provide a display mode to omit these nodes from the listing. Such a mode might be useful, when there is a high number of cluster nodes (more than one page), but I am not sure if this is somewhere needed.
It would also be possible to distinguish between short network separations (short times of lost reachability) and final deletion (when one scales a cluster up and shrinks it down later, without any intention to re-include after a network separation these nodes). Maybe this is what you are looking for?
