My elderly father is experiencing phantom smells that are so real to him he is leaving his home in the middle of the night - no one else can smell the?

Not normal. This is not normal and should be investigated. Seizures, tumors, and other serious problems can cause hallucinations of smell. He should see a neurologist as soon as possible.
Phantom smell. This is abnormal. Your father needs to see his doctor or a neurologist to be examined. This phantom smell could be a sign of several types of brain pathology e.g. Brain tumor. He needs examination and tests.