Judah is describing to Joseph a realistic but hypothetical case of what he will expect will happen to Jacob when he returns without Benjamin. (See: [[rc://en/ta/man/translate/figs-hypo]])
The father saying he would die if his son died is spoken of as if their two lives were physically bound together. AT: "since he said he would die if the boy did not come back" (See: [[rc://en/ta/man/translate/figs-metaphor]])