Most people would have better benefits. Some people would make more, some less. Some work would be moved to other less unionized countries, possibly resulting in more unemployment. Businesses would make less profits, some might go out of business. Prices would rise. The earth would continue to revolve around its axis and move around the sun. The world would adapt and life would go on.
But it'll never happen. I think we may see a rise in union representation as an outgrowth of the "Occupy..." movement, when they see if as a way to address some of their issues. But it would never get to 100%