▼ The construction uses the imperfect tense followed by the infinitive absolute, יָמוּת מֵת (yamut met). Because the verb is in a conditional clause, the emphasis that is to be given through the infinitive must stress the contingency. The point is “if someone dies – unexpectedly.” The next words underscore the suddenness of this.

▼ The verb is the Piel perfect with a vav (ו) consecutive; it continues the idea within the conditional clause.

▼ The expression is figurative for the vow that he took; the figure is the metonymy because the reference to the head is a reference to the long hair that symbolizes the oath.