I would have left as soon as they told me it was a mandatory evac.
If not I am quite sure I can come up with something that would float enough to get my family to safety. But then I have lived mostly in the middle of the great outdoors all my life and could be a little more enterprising than most.
Taking a look at your profile page, there's not much doubt in my mind that:
1. You would have had the sense to leave at the first sign of the impending disaster.
2. Living as you have you'd be able to get out on foot if it was necessary.