What happens to the musIQ harmonies if I stop playing the guitar and sing a capella for a while?
In general musIQ harmony will work fine if you do this. musIQ will use the guitar chords you have been playing before your a capella section to make good harmony choices that will fit in with your song. If you want to have more control over the harmonies that are generated, then you can mute the guitar after the musIQ harmony engine and strum chords to direct the harmony voices.