But seriously, though, 300-400 years is an awfully long time. Sure, there are plenty of companies that have been around for 200 years or more, but we're kind of in the age of big company mergers, buyouts, and what have not.
More than that, though, the corporation is a shockingly recent invention. It really only goes about about 150 to 200 years, if you make some reasonable assumptions about what you want a Corporation to be (such as, limited liability, the ability to incorporate basically just by filling out forms and not requiring particular legislative oversight, free issuing of stocks and bonds; obviously, things called Corporations go back a long while, although the farther you go back the less recognizable they are to our current view of them). How long it's going to last is a really good, open question.
Corporations exist -- at least by one theory -- because the convenience of having an organization in place provides economies of operation which are greater than the economies they would get with smaller, disparate, units competing against one another. What makes a specific corporation ``efficient'' depends on the details of manufacturing, transportation, marketing, enormously many factors. It's almost impossible to guess what any of these factors will look like in four centuries.
There are companies that already have histories already several centuries long; generally, they're breweries, banks, and the Boards of Proprietors of East and West New Jersey. Since they've survived a healthy number of historic upheavals and radical new ideas of how to organize businesses, they probably bid fair to continue surviving. But, really, in a world where AT&T can be broken up and then re-merge in strange forms, where Pan Am can go out of business, where American Express can be brought to the brink of bankruptcy by salad oil, and where a single aggressive idiot can destroy Barings Bank, what can you really expect to last?
