If her dark tresses fall, there is a fear that in an instant, they will turn black-like death.

Mir Taqi Mir shares a profound fear here. The poet says that he isn't afraid if the gentle fragrance (saba) of her tresses (zulf) ever breaks, because that loss would be manageable. The true terror, the real worry, is that this beautiful, dark cascade of hair (siyah-mār) will eventually transform into something destructive—a weapon, or a source of inevitable trouble! It speaks to the overwhelming power and dangerous beauty of a beloved's presence.