Do elderly people always die soon if they decline fast?

Definitely NO!: This depends entirely on the cause of decline. For example, my 83 yo mother experienced a sudden dramatic decline in health in january. She was diagnosed with polymyalgia rheumatica & with appropriate treatment is now doing quite well. Not all causes are as readily treated. A thorough medical evaluation needs to be done to find the cause- it could be as simple as B12 deficiency or be irreversible.