Question about DB connections

If I was to redefine the db connection as below, would that leave the original connection open or close it ? I am trying to switch between databases, the host could also change ie. master/slave

    DI::getDefault()->set('db', function ()
        use ($db_host, $db_username, $db_password,$db_name)
    {
        $connection["host"] = $db_host;
        $connection["username"] = $db_username;
        $connection["password"] = $db_password;
        $connection["dbname"] = $db_name;
        return new DbAdapter($connection);
    });

    DI::getDefault()->set('db', function ()
        use ($db_host, $db_username, $db_password,$db_name2)
    {
        $connection["host"] = $db_host;
        $connection["username"] = $db_username;
        $connection["password"] = $db_password;
        $connection["dbname"] = $db_name2;
        return new DbAdapter($connection);
    });