Cliff, et al,
There is another thread in turning a Chris Reeve One-Piece line knife into a spear here:
http://www.knifeforums.com/ubb/Forum25/HTML/000162.html
There was an older thread on this issue somewhere that was more extensive, but I have not found it yet. Someone there also raised the issue of knife damage and cost, but the poster said money was not an issue. I would like to find out if it was made. Can anyone find that thread?
One person had a good idea in the execution of such a project (unintentional but self-appreciated pun). That was to extend the tip all the way into the knife, with the threads back the appropriate distance. This would make the connection stronger and distribute any stress better.
Regarding survival aspects, I doubt anyone on this forum would only have one knife, but if they did, then they could make the appropriate decision as to the possible consequences. I know "The Edge" was just a movie, but I think I might have risked my knife, rather than rely on a fire hardened spear against that bear.
Personally I like the idea for an optional thrusting (not throwing) weapon or cutting tool. Further, re Greenjacket's comment about not carrying too much excess, the more uses one can find for something the better. How many people are going to carry around the appropriate spear tip, unless they have planned on doing some throwing.
A bayonet is anyone's last choice, but if you had whatever is used for affixing it to the gun, with a thread that fit the Chris Reeve knife, you now have a great field knife and a sharp bayonet. Since a field knife will see considerably more use than a bayonet, better to have a good field knife. (Caveat: I am not and never have been in the military, so this comment on bayonets is conjecture, but from what I have read, I believe it is a reasonable comment.) Further, it would be one more justification for carrying the knife in military service, if a reason was needed.
Now, who will tell us the thread pattern needed? If I see any walking sticks on the trail with threads just donw from the top, I know what conclusion I will draw, and I'll start looking for that Chris Reeve One-Piece knife.