Complex sentence: Former vocalist Chris Barretto had nearly finished recording the album before he left months before its release, so the band decided to rerecord Barretto's songs with Spencer Sotello.
Split into simpler sentences: Former vocalist Chris Barretto had nearly finished recording the album before he and the band parted ways months before its release. Rather than release the songs with Barretto's vocals, the band decided to rerecord Barretto's songs with Spencer Sotello.