Groo's nailed it right there. PSK's are short term survival aids only. They're used to help a person survive until help arrives, or until one can make their way "out".

As you touched upon, trailrider, Long Term Survival is also going to be relative to the locale one finds themselves within.

The most time I ever existed in such a situation was 7 days during a "training exercise". It was in a prime spot in the Blue Ridge mountains. To this day I still say God, Luck, Ancestral Spirits or whatever you prefer were on my side because everything went right, especially where procurring food was concerned. At one point I made a joke about throwing together a tripod and working up a fire to dry all the meat I was getting and the "instructor" made a face the likes of which I hope never to see again.

It also would have been a very different story if during that time I would have been required to be on the move

In any case, if it appeared that I was going to be in an LTS situation, my BOB would be with me, and I think my plan would be to make it to a spot where year round survival would be a somewhat easier prospect.