Did the onceler stop making thneeds after the swomee-swans and humming fish had left?

Yes, the Once-ler stopped making Thneeds after the Swomee-Swans and Humming Fish had left. As the environment deteriorated and the creatures disappeared, he realized the impact of his actions on the ecosystem. The loss of the Swomee-Swans and Humming Fish made him recognize the unsustainable nature of his business, prompting him to cease production. Ultimately, he understood that the health of the environment was more important than profit.