How do config servers know if replica member has been removed?

For example, assume:

- replica set consists of r1.replica.db, r2.replica.db, r3.replica.db
- config server adds this replica set as a shard using

1) log into member of replica set and use rs.remove(r3.replica.db)
command. Assume r3.replica.db is not the Primary
2) log into config server and type db.printShardingStatus(). You still
see a reference to all three members:

shards:
	{  "_id" : "shard_1",  "host" : "shard_1/r1.replica.db,
r2.replica.db, r3.replica.db" }

What happens now? How does the config server know that r3.replica.db
has been removed?

Thanks in advance!