God I'm tired of hearing this platitude. Define "Fine" when 90% of the animals on earth are extinct? What is "fine" to you about that, exactly?
If humans go extinct, human timescales cease to be relevant. Since we're talking about the Earth, reverting to geologic timescales makes sense. Earth 10 or 100 million years after humans may not be that different with or without humans.
(I agree, however, that the platitude is unhelpful. We're human. We care about the Earth on a human timescale.)