I didn't think I got much past turn 20 and had 2 upgraded walls but I think 3 of my guys died to attackers. The first one starved because I wasn't paying attention.
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up until turn 20 your people can only die of starvation, after the 20 days then they can be attacked. pretty unlucky if you lost them all very shortly after the 20 days.
Just end the game over scene then have another go at it you might have better luck on a second attempt. notch it as that small survival family lost the battle as many would in those circumstances.