Happy birthday is actually still under copyright, but it's a bugger to collect all the fees.... Besides, eveytime you insert person's name, you change it slightly so you can get away with it..... I daresay it will still be sung in 1000 years, assuming we haven't blown the planet up, or decided that birthdays are ageist, and discriminatory against those cultures who don't celebrate the anniversary of the day they were born....I'd like to think we'll still be singing Old Lang Syne, but as I personally haven't sung it myself for 14 years, suspect that it could be dying out.
LTS