▲这不是疑问句，而是虚拟语气的省略形式，即原句相当于：

Had we not missed the plane, we would all have been killed in the crash.

=If we had not missed the plane, we would all have been killed in the crash. 

要不是我们错过了这班飞机，我们就都死于这场事故中了。

▲你的句子省略了 if，并把 had 提到了句首。又如：

Had he succeeded, he would have acquired a monopoly. 如果他那时成功了，他就会获得垄断地位。

Had we not missed the plane, we would all have been killed in the crash. 要不是我们错过了这班飞机，我们就都死于这场事故中了。

Had we known about it earlier, we could have warned people of the danger. 假如早点知道这件事的话，我们就能警告人们有危险了。

Had he lived up to his promise, he would have made a fortune in sponsorship money. 要是他遵守了诺言的话，他本应该已经从赞助费中赚了一大笔钱了。

Had she kept the camera focused on the river bank she might have captured a vital scene. 要是她把相机的镜头一直对准河岸的话，可能就捕捉到重要的一幕了。

▲相关知识内容，请参考：

http://www.yygrammar.com/Article/200905/1208.html 

http://www.yygrammar.com/Article/201204/2859.html 

http://www.yygrammar.com/Article/201205/2942.html