would be worse

-Our only chance of safety lay in making a clean job of it, said he, and he would not leave a tongue with power to wag in a witness-box. It nearly came to our sharing the fate of the prisoners, but at last he said that if we wished we might take a boat and go. We jumped at the offer, for we were already sick of these bloodthirsty doings, and we saw that there would be worse before it was done. We were given a suit of sailor togs each, a barrel of water, two casks, one of junk and one of biscuits, and a compass.
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The problem here lies with the meaning of IT in IT WAS DONE; my first impression was that IT would mean the act of being given an offer, which means if they had not accepted the offer, they would have been killed. But in that case, the sentence would be

-we saw that there would have been worse [things], before it [=the offer] was/had been done[=accepted]

What do you think the red sentence means?