Determine if block has already been registered

EDIT

I just realized you’re doing this on the PHP side. There is a class called WP_Block_Type_Registry that you can use to see what is already registered:

$registry = WP_Block_Type_Registry::get_instance();
if ( ! $registry->get_registered( 'foo/column' ) ) {
    // YOUR CODE
}

Gutenberg should fire a console error if a block has already been registered. See the registerBlockType src here.