Complex sentence: The Limbourgs'career ended just as van Eyck's began-by 1416 all the brothers (none of whom had reached 30) and their patron Jean, Duke of Berry were dead, most likely from plague.
Split into simpler sentences: The Limbourgs'career ended just as van Eyck's began. By 1416 all the brothers (none of whom had reached 30) and their patron Jean, Duke of Berry were dead, most likely from plague.