Question

George would certainly have attended the proceedings___，

为什么不是 if he didn't get a flat tire
而是had he not had a flat tire.

不是应该选带有if的那个么？ 改成 if he hadn't got a flat tire 对吗？

Answer 1

因为是虚拟语气，要表示假如过去某件事与已发生的情况相反，就应该用had done“要是（之前）有……”或had not done“要是（之前）不是……”的形式；一般写成if he didn't get a flat tire也没错，但因为这一句前面已经用了一次虚拟would have attended，所以后面应该一致；
had he not had a flat tire是省略句，可以等同于if he hadn't got a flat tire