Severus smiled fondly. Stressful as his life had been those last few years, and strict and disliked as he was as a teacher, he actually had enjoyed teaching. At least, he'd enjoyed it when he had eager students as Miss Montgomery had been. And he'd very much enjoyed trying to be the voice of reason and opportunity among his students, fostering their interests and helping them to make connections for careers. It wasn't always successful, but he took pride in the fact that the Dark Lord was annoyed with him for not bringing more recruits into the fold, that fewer of his Slytherins had taken the Mark than Slughorn's.
He couldn't save them all. There were notable and heartbreaking exceptions - like Draco - but for the most part, none of his Slytherins went to the Death Eaters because they had no other options. If they made that choice, he couldn't stop them, but he made bloody well certain that it wasn't their only choice, as it had been for him.
"You were a delightful student. I'm sorry to admit I can't recall the career path you were considering? I clearly remember that there were no doors closed to you - your marks were high and you were universally popular among the teaching staff. Do you know what you eventually chose for a career?" Many people here did know things that ought to have been a mystery, after all, due to the nature of the comings-and-goings of the populace.