I imagine the answer is that they would eventually spread much like the original spread of humanity. Much of our technology is so complex that it would be entirely unusable or irrelevant to the new explorers.
Of course it would still give them a head start, since our houses, workplaces and whatnot would already be present, however the real advantage would be in agriculture. The start of agriculture was key to the advancement of humans because we settled down in order to tend our farms, built cities and civilisations, and having gone almost nowhere in 160-260 thousand years of hunting and gathering (the first biologically -us- humans are about that old, while agriculture as we understand it isn't more than 12-14 thousand years old), we suddenly began to advance very quickly once we had permanence and agriculture.
Giving the uncontacted tribes access to our cultivated plants, our fabrics and textbooks could very well mean that what took us thousands of years to learn would take them a very short time indeed once they learnt the languages of our modern world.
The groups that refused to go may well continue to live just as normal. While a lot of jobs wouldn't be filled, we wouldn't need so many to fill them. I imagine that we'd group up, because it's both core to our psychology and essential in order to keep using the relics of our age, like the water treatment plants and steel foundries. Groups that cut themselves off before would likely continue to do so largely unchanged.