这是个不是实际的假设,应该用虚拟语气,是：
If we had been dead,we would not enjoy our life any more.
5楼的have been dead不是被动语态,楼上的说错了,因为dead是形容词,不是die的过去分词died,但life不应用复数,且life的复数形式是lives而不是lifes