A song isn't worthless because it ends. The value of a life is more than its end result.

Well if the song dies/it's lost it's pretty much worthless.

I don't think anyone really evaluates a song on whether they think it'll survive the lifespan of the universe. It's a very narrow definition of value.

There would be no song to evaluate once it dies/is forgotten. Of course it could have some value for the people that heard it but that values goes to zero once they die as well.