Palliative care is an amazing thing for patients, their families and friends. This guy does sound like he is at the terminal phase of his life. As a nurse you have the honour of ensuring that he is comfortable on your shifts. Even if he can't talk use you non verbal skills to assess if he is in pain and medicate appropriately. If he is very gurggly reposition him after pain relief to help with the secretions.
I am guessing that you are not on your own - you have an EN or AIN who has probably much more experience than you with this situation. Follow their example, if you notice a change on your shift call his family and update them, even after 12 years it is hard to guess when someone will die - I have seen someone who was phase 2-3 just go to sleep and never wake up and a lady at phase 4 for 10 days. I always say I will call you unless they don't want to be contacted.
When he does die there is no need to panic, he is not in pain anymore. If you are the first there, check to confirm by looking for a pulse for 1 min. Take note of the time and document it. Follow policy around notifying the doctors, your manager etc.
Treat him with the same respect post mortem as you did when he was alive, I talk to the patient, explain that I am washing them (warm water), tell them I am putting them into the shroud and body bag. I wish them well for whatever is next.
Sometimes I am sad, distressed or at peace - usually depending on the way the patient was cared for before they died I get distressed with families that don't want their loved one to be "doped up" and they die distressed, I am sad if it a person or family I have known for a period of years (chronic liver), I am at peace if the patient has made peace with their death. There are not a lot of Aussie nurses here. Have a look on FB for The Nurse Path and New graduate nurse pages....one of my grads set up the VIC new grad page that has 100s of members.
Discuss your concerns with your manager and ask for assistance.