Severus tried his best to block out the consequences of his unsuccessful mission because no matter how much he happened to dwell on it, it obviously would not change how the events had laid out for him. All he could do was brace himself for the Dark Lord's punishment. Or perhaps he could get to the kid before the Dark Lord found out... He quickly ruled this as impossible and instead watched gormlessly as Rabastan set the hedge alight.
"No, I'm going to go straight home. Thanks for accompanying me."