I think Spotify will die in 5-10 years, but not because of royalty fee woes. We will not go back to the "buy a song for $1" model of the early 2000s. But it will die because of the moonopolistic and anti-competitive practices of the popular OSes: Apple preinstalls Apple Music, Google Play music, and Microsoft Groove (all 3 clones of Spotify). This agressive, monopolistic behaviour will kill Spotify, just like MS riva…
I think youtube is its biggest competition to be honest. Because youtube has a frictionless method of payment (ads), has a paid option if you don't want the ads and is massively useful for "discovery". I could see youtube killing Spotify and all its competitors.
Also Google doesn't want to cannibalize their own Play Music sales.