Well, well, well. The truth is finally coming out. And he'd been right all along! Obviously.
Dumbledore will have ways of tracking Lupin, surely; the old man doesn't trust anyone as much as he pretends to and Lupin is a marauder and a werewolf. The most untrustworthy breeds of 'man'.
The only real dilemma is whether he should call the ministry before or after going to Dumbledore. After all, the headmaster is very free with his second chance nonsense. And Severus doesn't want to miss a chance to see his nemesis suffer the dementor's kiss.
This is shaping up to be the best day of his life.