Not long. There is no rule for this, it just is a signal of EOL. Eventually, he will probably quit asking for any liquids and then it's really just a matter of time.
Just keep him comfortable and let him know he's loved. Help his transition into the next life be peaceful and calm.
Even minimal fluid intake can prolong from one week to one without any fluid to one month with it. Your best guide will be the hospice people caring for your loved one as they are the one who knows the patient best at this point, what they fat reserves are, what their body has adapted to. You would be amazed how long the human body can go on with very little nourishment. I am sorry for the struggle and your approaching loss.
Unfortunately, probably not long. It sounds like he is at the end of life. Try and get him to tell you the things he loved about his life. Show him love and compassion. Tell him the things he did that made you proud. Hold his hand through it all.
Just keep him comfortable and let him know he's loved. Help his transition into the next life be peaceful and calm.
my dad is also the same.
I’m doing everything Diana says.
sending love to you all