All Those are excellent points. Still there must have been some level headed Coneheads with common sense. Even given weeks or months of seperation of groups, and giving the pressures and trauma, I think it would have occured to one or two of the Coneheads that there may have been other survivors. I don't believe Cutter after 10,000 years was the first elf to think "gee are there other elves out there?" Also in the picture linked to by Vojira if the shadows were others THEY WERE WITHIN SHOUTING DISTANCE of the Eight
I myself have zero survivor instincts and skills, but I hope I'd have enough sense to shout for possible help if I were in their shoes.