Watch his mail. Once he starts missing payments overdue notices arrive and you can get a decent handle on who he owes. You might get bank statements if they still mail them. Similarly, try to get on the good side of someone at his bank; this isn't easy before he passes, but after he expires if you're the executor/administrator/whatever title the bank can get helpful. Once you get a handle on where his money goes you're halfway home. Yes, you can negotiate with his debtors, especially on unsecured loans. Fifty cents on the dollar is a lot better than nothing on the dollar.
Everybody notifies the government when someone dies. Hospitals tell Medicare, S.S., board of elections, and the state. Funeral directors get in on it too.