譬如What if I came tomorrow instead of this afternoon ?

只有一個條件從句，那它的主句就一個what?還是省略了什么？

費致德《現代英語慣使用方法詞典》對“What if...?”有以下講解：

What if...?的意思是：

a.“假如......那就會......嗎？”（What will happen if ...? What is the case if ...?）有時用虛擬語氣，如：

Let people speak up, the sky wont fall and neither will you. What if you dont let people speak? Well then, you are pretty sure to tall one day. 叫人講話，天不會塌下來，自己也不會垮臺。不叫人講話呢？那就難免有一天會垮臺。

What if you go instead of me?（What would happen if you went to my place?）

b.假如......那又有哪些關系呢？（What does it matter if...?），如：

What if it is true?（What would happen, if it be true?）假如那是真的，又如何？

What if he does not come?他不來又有哪些關系？