public Set<T> getDepartedMembersSet() {
    synchronized (memberToVersion) {
      Set<T> result = new HashSet<>();
      for (RegionVersionHolder<T> h : memberToVersion.values()) {
        if (h.isDepartedMember) {
          result.add(h.id);
        }
      }
      return result;
    }
  }
Returns a list of the members that have been marked as having left the system.
geode-core/src/main/java/org/apache/geode/internal/cache/versions/RegionVersionVector.java