He struggled through a period of serious depression, but bounced back after awhile to continue painting after his wife's death.
From the Wikipedia:
Chagall took inspiration from Belarusian folk-life, and portrayed many Biblical themes reflecting his Jewish heritage. In the 1960s and 1970s, Chagall involved himself in large-scale projects involving public spaces and important civic and religious buildings.
Chagall's works fit into several modern art categories. He took part in the movements of the Paris art world which preceded World War I and was thus involved with avant-garde currents. However, his work always found itself on the margins of these movements and emerging trends, including Cubism and Fauvism. He was closely associated with the Paris School and its exponents, including Amedeo Modigliani.
His works abound with references to his childhood, yet often neglect some of the turmoil which he experienced. He communicates to those who view his works happiness and optimism by means of highly vivid colors. Chagall often posed himself, sometimes together with his wife, as an observer of the world — a colored world like that seen through a stained-glass window. Some see The White Crucifixion, which abounds in rich, intriguing detail, as a denunciation of the Stalin regime, the Nazi Holocaust, and all oppression of the Jews.