You can't make a dead man pay anything unless there's some sort of contract involved that accounts for these sorts of situations so it will be up the people who he owes money to try track it down but I doubt that will be very fruitful unless he put some safeguards in place or left instructions to his next of kin on what to do. How do you know he actually passed away?
It seems to me that the loan were from DarkStar_. In the forum I do not think when a person to person lending is in operation the lenders are asking if you die then your relative needs to repay it and such thing. Considering the no term, the lender has always risk to lose his money.
In some cases maybe the relatives are not aware too that their died family member was on this forum and they have xyz amount of debt to someone.
Question remains was it a collateral loan?
In that case the lender has something to cash out but if this was a no collateral loan then it's a lose the lender have to accept. That brings the last part, should he tag the account? The dead person is never coming back. Leaving a negative will not change anything except in the long future people who will visit the profile they will see this person scammed a loan which clearly was no correct.