The full stop is not added where the dash marks an unfinished sentence. But it is common to add the point of interrogation or the mark of exclamation.
XLI. The dash is used to mark a faltering or hesitating speech.
Well—I don't know—that is—no, I cannot accept it.
XLII. An unexpected turn of the thought may be marked by the dash.
He entereth smiling and—embarrassed. He holdeth out his hand to you to shake, and—draweth it back again. He casually looketh in about dinner-time—when the table is full. He offereth to go away, seeing you have company—but is induced to stay.
French history tends naturally to memoirs and anecdotes, in which there is no improvement to desire but that they were—true.
XLIII. When the subject of a sentence is of such length, or of such complexity, that its connexion with the verb might easily be lost sight of, it is sometimes left hanging in the sentence, and its place supplied by some short expression that sums it up. A dash follows the subject when thus abandoned.
Physical Science, including Chemistry, Geology, Geography, Astronomy; Metaphysics, Philology, Theology; Economics, including Taxation and Finance; Politics and General Literature—all occupied by turn, and almost simultaneously, his incessantly active mind.
The colon is sometimes used in such cases; but the dash seems preferable, as it is the point that marks a change in the structure of a sentence.
XLIV. The dash is sometimes used instead of brackets before and after a parenthesis.