public static boolean isUnassignable(State state) {
    return state == State.MERGED || state == State.SPLIT || state == State.OFFLINE
      || state == State.SPLITTING_NEW || state == State.MERGING_NEW;
  }
Check if a region state is one of offline states that can't transition to pending_close/closing
(unassign/offline)
hbase-client/src/main/java/org/apache/hadoop/hbase/master/RegionState.java