Life support is being discontinued...?

It depends what kind of life support, if it's lungs like a tube down the throat, then what happens is there is no more air going into the body, the little air in there keeps the heart beating for a few minutes then the person is just gone, dead. Usually the person is in a state near death or brain dead when that happens and there is no pain or anything.

I have been a nurse in nursing homes for 33+ years so I can tell you that it can be any where from a day or two up to a week or more before he will pass away. Death is one thing that can be very hard to predict. Make sure they keep your dad comfortable and if you notice he is restless at all or moans at all call the nurses and ask for medication. If you have not involved hospice I would encourage you to talk to your dads hospital social worker in the morning about this. They are wonderful. I wish you all the best and may god make his final journey a peaceful one.