But if it had to perish twice,
Here the conjunction "But" is a word that introduces a change. We know that he stated one thing, and now he might possibly be switching because of "but". If the speaker was going to stick with the initial decision and just add on to it, the correct conjunction would be and. If the speaker was still trying to decide one way or the other, the speaker would use the conjunction "or". "But" shows the speaker changing his mind.