Sorry I missed your post last night. I am even sorrier for your pain - and your father-in-laws condition.
By the time you read this he may in fact have left this earth. The end often comes suddenly, even after days or weeks of going through the final stage of the dying process. It's not predictable until it is. You'll know what I'm saying when the time comes.
If you haven't read the information regarding death that is offered by Hospice I encourage you to do so. It's very informative. If it hasn't been supplied, ask for it.
No on has come back to tell us if these final days are suffering even when pain is well controlled. That said I have been very close to death several times, indeed the last time my family was told I would probably not make it through the night(s). This condition went unchanged for three days. Obviously I recovered. Similarly my mom was once so ill with Influenza A that she had to be vented for five days.
During the above times that I describe I did not truly suffer. I was ready to leave this earth and I had good pain control. It was a very difficult time for my husband and loved ones. I've always said and believed that often these times are more difficult for our loved ones. It was true for me.
My mother had absolutely no recollection of the days she was so ill leading up to the vent - or for the first day off it. She too did not think she was "suffering".
I believe in a Higher Power - I have to in order to survive in this world. I believe too that when our time comes He prepares us.
Hang in there sweeite and be supportive. That's all you can do at this point. Your father-in-law's children and wife (if he has one) will need you. Being strong is very over rated - be sweet and compassionate - be understand and kind - offer prayers if welcomed.