are blowguns viable survival weapons?
No not at all IMO, I have actually shot game with a blowgun, several times, with very poor results. A field expedient bow and arrow is much better, or better yet, Doc's snares. Hell, even a rabbit stick is better.
Also, unless your talking about a TEOTWAWKI situation, getting lost in the woods for so long that you need animal food is a bit of a stretch, if you can walk in a straight line you can walk out of practically anywhere in the lower 48 long before you are at risk for starving to death. If you can't walk you more than likely are not going to be rambling around hunting with a blowgun.
If it is a TEOTWAWKI situation I suggest that you arm yourself with something much, much more efficient than a blowgun. Chris