Something or someone is completely finished, defeated, or dead. The precise meaning of this phrase depends on the context. In This loss means that it's all over with the company, it refers to defeat, whereas in The vet can do no more; it's all over with the dog, it refers to the dog's death, either approaching or actual. Also see all up (with).
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.