Unless something unexpected happens, I'll see you tomorrow.

如果不出意外，我明天去看你。

《牛津词典》

What will you do if anything unexpected happens, like heavy traffic or a sudden rain?

如果有意外的事情发生，比如交通堵塞或突然下雨，你会怎么做？

youdao

Get nervous when something unexpected happens or things go wrong.

当有意外的事情发生或事情出错时要紧张起来。

youdao

Because virtually no one, perhaps with the exception of 1 percent of the population, can afford the massive cost if the unexpected happens.

MSN: Health insurers seek to soften their image

Very few, I predict -- unless, of course, something unexpected happens.

WSJ: Shattering the Bell Curve

But sometimes in any election, the unexpected happens.

BBC: Nottinghamshire PCC: Pledge to help victims