Don't you have a feeling that the users of every world language thought that theirs would be the one to last? Didn't Latin have its roots in Sanskrit? And would not a medieval German monk (or indeed, an English monk) have found it, at best, amusing if you were to suggest to him that one day English, that mongrel tongue, would become a world language? Nicholas Ostler (he of "Empires of the Word") has argued that English too, will eventually give way to another language. Of course, the time scale on which this happens is measured in millennia, and on that time scale, English is a very young language: no need to rush out and learn anything but English, in our lifetime.