You could do that anyways. Although the physics are client sided, the server can still tell the client that the bricks were 'killed' and can be used as a physics brick. However, the physics brick cannot do anything but move around and look pretty, the server doesn't even think it's there. However, if it were server sided, a high speed physics brick could perhaps kill someone, 'kill' other bricks, and you could probably even walk on them, rather than having them scatter when you land on them.
