I do not know exactly him even have read his post and his thread. so what makes me interested is, what happen with his lending, does he still have to pay?, give it up?
He obviously can't pay for his lending anymore if he is dead, and it's up for the guy who lend him coins what he is going to do.
Some family members could probably pay this if they inherit his account with Bitcoin and will instructions, but I wouldn't count on that, and I don't like the idea of inheriting accounts.
But about the legality, their family, spouse or friend have no legal obligation the debt in most cases. It's different case if that person wish to keep asset which isn't fully paid yet or cosigned a loan with the deceased one.
Any debt is usually passed on spouse or other family members, but I have no idea how this would apply for coins someone borrowed in bitcointalk forum.
Legality of this is not cleat in many jurisdictions, and people could also remain private, not connecting bitcointalk account with their real identity.