What is the next step?

Platinum, this is something that the next of kin (his son) has to decide. I’m sure that any decision he makes about his father at this point isn’t an easy one for him or any other family your friend has. You are his friend, but unfortunately you don’t have any say and I know this is rough on you. I’m sure that the doctors and nurses are monitoring your friend and they know if he seems to be in distress. They will do all they can to keep him comfortable. But again, the doctor says they can’t wean him off the ventilator so his son says keep him on it. That’s their decision. Again, I’m sorry for you...and your friend.

I'm so sorry about your friend.
If his kidneys are failing, it is very likely that his body will start shutting down. Most likely, it won't be too long. (Without more information on the prognosis /diagnosis.)
There are many different options /circumstances. Doctors can recommend shutting all the machines down, because in their opinion there isn't any hope of improvement or recovery. But they can be challenged / overruled by family, who doesn't want to give up just yet.
A similar thing happened to a family member of mine. But once his kidneys started failing, the family realized there wasn't much hope. And made the terrible decision to turn the machines off.
Again, I am so sorry.

More info is needed...does your friend have an advance directive (sometimes also called a living will)? Also, does your friend have a medical Power of Attorney or a legal Guardian that has been appointed to make medical decisions on his behalf? Lastly, what are the doctors recommending?

I’m sorry to hear about your friend. However, unless you have Medical Power of Attorney for this friend, it is up to his son to make the decision whether or not to take him off the ventilator. The son is following the doctor’s advice which is what he should do. No one can say how long your friend will be in that state. The next step is to keep following the doctor’s advice.