What if--?

（仮に）

もし--なったら。。。（どうする？）

もし--だったら[もっと悪かったでしょう]

Examples:

1. A: We had better ask him about this right away.

B: Yeah, but what if he lies about it?

2. What if there was a well qualified woman who applied for the job. Would you hire her?

3.

I'm sorry. I know you're shocked. I didn't want to tell you. But what if nobody had told you.
You would never have known that your husband has been cheating on you.