(よ)うものなら
文法の解説は英語です。
用法
Used to express 'something that shouldn't be happened and the unfavorable situation when it happens'
言おう + ものなら
例文
彼女との記念日を忘れようものなら、１週間は口を利いてもらえないだろう
If I were to forget our anniversary, she probably wouldn't talk to me for a week
浮気がバレようものなら、離婚は免れないだろう
If my affair were to be discovered, divorce would be inevitable