The prognosis is unknown for your friend's husband at this time. It depends on whether or not there has been any neurologic damage. Sometimes with an infection and swelling, there is only temporary injury and the nervous system will recover in time. The time frame you gave is not too long for complete recovery (assuming the correct diagnosis and treatment is rendered).
That brings us to 2 more questions. One is how certain they are of the diagnosis (they had missed it before). It does sound like he has some sort of encephalitis, but what is the cause? I assume they had done blood cultures and spinal tap with cultures to come to the diagnosis. Many things can cause encephalitis, like West Nile or gonorrhea, etc.
Finally, if he has Herpes Encephalitis, why should he have contracted this disease? Usually, a healthy person with intact immune system does not get this.
They are not certain of the diagnosis I think as all the tests have returned no results other than increased white blood cells and a second scan showing swelling this is what they think it could be. The hospital where he is located is a small orthopedic hospital and they say he needs to be transferred to a hospital that specialises in head trauma. Unfortunately there are not enough beds available and they have to wait to see if one comes available in the meantime they do not seem able to find what is causing the problem.
He is generally fit and active, he does smoke and drink, this is a very close family friend and as far as I am aware he has no other health problems other than suffering from depression in the past. He has been under quite a lot of work related stress in the last year and two weeks ago his father died suddenly after been misdiagonised at a doctors surgery collapsed on the street outside the surgery and died in hospital less than an hour later having suffered a massive heart attack. Can on going stress like this reduce the immune system enough to allow such a condition to develop.
The reason I decided to ask is because my friend is being told the prognosis is not good and I wanted to know how long an untreated patient can last before this conclusion can be arrived at.
Stress is a grossly underestimated factor in illness and healing; however, to get Herpes encephalitis (if indeed he has this) requires something else more than just stress. Certainly, the prognosis is unknown; but if the diagnosis is not confirmed and he is not treated appropriately then is definitely would be poor.
If the cultures don't confirm the infection, then he may need a biopsy.