If depends on what you mean by 'preserving'. If you want to take a snapshot of the information, and keep it accessible, then the usual web archives can help.
But if you want to keep it expandable - dynamic, interactive and growing - well, by some definitions that's not a preservation matter, but a matter of cultivation. In the near term, DPQA is fine just being hosted by the Open Planets Foundation, but with an eye to the longer term, it would be good if a larger group of organisations committed to it. This is also the idea behind the COPTR site.
A sensible middle-ground might be to provide data dumps of the contents of this Q&A site, so that if it does die, any future effort has somewhere to start. After all, that's part of the story of how this site began.
UPDATED to add some ideas about sustainability.