要不然 (yào bù rán) indicates if not, or otherwise. It often appears at the start of a sentence. See the example below:
要不然我就家破人亡了. (yào bù rán wǒ jiù jiā pò rén wáng liǎo). This means otherwise/if not I will lose my family. Maybe the sentence, or clause that precedes it will indicate some change that is necessary in this person’s life.