It actually can't be `false`: https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/storage/BlockManagerSlaveActor.scala#L44. I think this is intended to be some sort of ack. The executor's BlockManager actually has another mechanism of reporting this removal to master. Otherwise, the master is not concerned with whether the block was successfully removed.

(We may or may not want to change this design)