Future Harry reassures himself that no Death Eaters could have survived Voldemort's downfall, since the Dark Mark would kill them all when the bearer of the master mark died.
But hang on - the mark is inscribed on the body, and Voldemort's original body did die, when Harry was an infant. Why didn't the Death Eaters all pop their clogs then, and how come his reborn body bears the master mark?
(Note that the whole master-mark-kills-others setup is a departure from canon, so that's not broken either way.)