I wouldn't worry about Digitrax, NCE, or Lenz going under. The only possible way that could happen is if the founders die unexpectely, like Don Wangrow did. Each of the three have solid folks running the place; AJ and Zana Ireland at Digitrax, Jim Scorse at NCE, and Bernd Lenz (or, Stan and Debbie Ames in the US) for Lenz. So, unless these folks get bored and decide to become hermits or something, their companies should stick around.
The other issue related to this is that since their user bases are so large, they could be candidates to be bought out in that event, and they would continue to operate in that manner.
As far as decoders go, the only Digitrax decoder I use is the DH163LO, for the P2K locos. It has the 1.5v transformer on it, so I don't have to swap out bulbs (I hate doing that, period!). I have one of their new Sound FX decoders on order, just to see what they're like. But, for the rest, I use TCS, NCE, Soundtraxx, and Loksound. I have a couple of Lenz ones sitting around, plus 2-3 already in locos.
Kennedy