"It may then behoove its owner to suspend maintenance and keep the otherwise obsolete plant in production. "
In this case "plant" means a piece of machinery used in manufacturing a product.
The text says that although the plant is obsolete (out of date) and not financially efficient, the owner can save money by not maintaining it (not repairing and looking after it) properly, and keep it producing things for a while longer. The text then goes on say that this can only be a temporary solution as the lack of maintenance will cause the plant to break down eventually.
keep the otherwise obsolete plant in production
= make the plant, which is actually out of date, keep on producing things
not a teacher