conjunction followed by conjunctive: 要不是yào bú shì…就jiù…
要不是下雨(的话),我们今天就出发了。
Yào bú shì xià yǔ (de huà),wǒ men jīn tiān jiù chū fā le。
要不是你提醒我(的话),我早就把那件事给忘了。
Yào bú shì nǐ tí xǐng wǒ (de huà),wǒ zǎo jiù bǎ nà jiàn shì gěi wàng le 。
Note that the negator 不 bù can of course be placed immediately before the verb in the same clause, without changing the meaning of the proposition:
要是不下雨(的话),我们今天就出发了。
Yào shì bú xià yǔ (de huà),wǒ men jīn tiān jiù chū fā le。
If it had not rained, we would have set out today.
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.