If someone in their 70's has kidney failure, double pneumonia and liver and heart trouble as well as colitis and dehydration, recovery possible?

Will to live. It is possible to recover. Okay to talk to your docs about your recovery. It will be a team effort and the patient's desire/will to recover is the most important factor. Don't give up.
Many things involved. It sounds like you are dealing with a complicated situation. It is possible to recover from complicated medical problems, but much depends on the individual's baseline health. Is this an acute illness, or has the person been chronically ill for a long time? "simple" interventions like rehydrating a patient, adjusting their electrolyte balance, and giving antibiotics may work wonders. Good luck.