This came to me while reading the "If everyone was your type" thread.
I was just thinking of how things might be if there weren't any NT's. The first effect I think people would feel would be a rapid slowdown in innovation. Technology would improve in slower, more predictable patterns, if at all.
Real innovations and solutions would give way to many temporary "kludges," because no one could really understand the underlying systems well enough to replace/redefine them easily, or directly address the "root" problem.
INFJ's, ISTx's, and ESTJ's would probably be forced to fill the gap as much as possible, and be frequently stressed by the constant need to use their tertiary/inferior functions, and would still be much slower and inefficient in their approaches, although they would likely manage to come up with something eventually.
Systems would break down right and left, and despite the best efforts of the above types, things would never work quite as well/smoothly on a large scale as they did before.
Society would continue smoothly on a local scale because of the SJ's, but problems would keep building and building over time, and it would take longer for them to be sorted out.
What do you imagine in such a world? Needless to say, I would miss them.