India is already getting too expensive. The Philippines is the hot place now, but wages are rising quickly there also. Companies could start to look to Africa, but the corruption and lack of a government in many of the countries makes that a tough move.

What will happen is as wages rise more and more work will simply be automated. Factories will be built where they most geographically make sense (close to components, raw materials, customers, etc...)

Expect to see mini silicon valleys of manufacturing pop up much like what happened in Detroit with automakers and part suppliers during the hey day.

Also, saying they aren't coming back is ignoring that they never really left. US manufacturing is still growing strong, and the main reason long term for more new factories to not be built in the US will have to do with the EPA more than labor wages.