While there's no denying illegal downloading of songs has a small impact on record sales, if everyone's ability to download said songs suddenly disappeared I don't think you'd see much of a spike in record sales. Put simply, 90% of the music out today just isn't worth the money.
So, you honestly believe that if the downloading of songs was impossible, then everyone would abandon their ipods, zunes, and what not? Perhaps, but then those people would return to the radio, raising advertising revenue and, in turn, the record companies' profits.
Most of the top selling albums of the 90's are just as crappy as what's being churned out today. Who ever liked listening to Whitney Houston, Alanis Morissette, Hootie & the Blowfish, the Backstreet Boys, Britney Spears, Celine Dion, Kenny G, Boyz II Men, Mariah Carey, TLC, MC Hammer, Michael Bolton, or the shit stains known as Creed?