Hi Branden,
This is expected. If the persistence is based on a cookie, the client could continue to present the cookie in requests for either the duration they keep their browser open for (for a session cookie) or until the time expiration is reached. If they're consistently making requests, a time expired cookie wouldn't reach the expiration time. Basically, you could disable the node to prevent new TCP connections and then after whatever grace period you want passes force it offline to prevent any new TCP connections or clients with persistence records from reaching the node.
Aaron