I think they're still around, outside of the valley. Fragmented and lesser in number but still there.
I also wanted to say, it's possible that Stranger isn't fully grown. Some of the grubs made a comment that he was "scrawny for a steef." And I also noticed that the mounted heads seem to be from larger Steefs then Stranger. Maybe he's just a teenager?
That could also explain the difference in size between documentary Stranger and game Stranger. Could be that they were using models of a more developed and adult Stranger from... dare I say it... Stranger II.
