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Faora: Zod disappeared and took the rest of out people with him.
We were wrong to follow you. When we did what you asked and tried to
assimilate with humans we were left behind. They didn't succeed or Zod
left them behind?

We're gathered here waiting for Zod's return to ask his forgiveness.
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Because it says "Zod disappeared and took the rest of out [presumably a typo for "our"] people with him", I assume it means they were literally left behind. That is, all the others moved somwhere else without them.

Another possible meaning is that they were left behind in terms of technological progress, or something like that. Without knowing more about the story it's impossible to be certain.
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Thanks, Mr Wordy!