除非 + Condition, 否则/才 + Result
除非 (chúfēi) means "unless" and introduces the only condition under which something can happen or change. As a preposition, it precedes the exceptional condition. It is often paired with 否则 (fǒuzé, "otherwise") or 才 (cái) in the main clause.
除非你亲自去,否则他不会答应的。
Chúfēi nǐ qīnzì qù, fǒuzé tā bú huì dāying de.
Unless you go in person, he won't agree.
除非下雨,我们就按计划出发。
Chúfēi xià yǔ, wǒmen jiù àn jìhuà chūfā.
Unless it rains, we'll set off as planned.
除非拿到签证,她才能出国。
Chúfēi nádào qiānzhèng, tā cáinéng chūguó.
Unless she gets a visa, she won't be able to go abroad.