I think you have it backwards (or maybe I do - it's getting late for me :) )

if (!fork) { die; }
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Should die only when fork is not true, that is 0 or undef.

Thus, it's either the child (which really doesn't make sense because a dying child is no big deal) or it's undef, which means something bad happened.

The first one, as you said, is your normal error. I didn't think that one was under question.