This is referring to iTunes Match. An opt-in feature where you would upload your own MP3s to Apple for them to host and where there is an option to replace those songs with high-quality versions from the record labels.
a) Your brother should have taken backups of his MP3s as he was advised.
b) He pressed the button to replace the songs because there is no evidence, anywhere of this happening automatically. And common sense suggests this is the case because there would be a lot more uproar if 10's of millions of users songs were suddenly disappearing at once.
a) Your brother should have taken backups of his MP3s as he was advised.
b) He pressed the button to replace the songs because there is no evidence, anywhere of this happening automatically. And common sense suggests this is the case because there would be a lot more uproar if 10's of millions of users songs were suddenly disappearing at once.