I don't remember anyone addressing dieing of old age, but AFAIK escaping the DR is supposed to give you your body back. Now even if dieing of old age lands you in the DR, escaping doesn't help you much. You will return shortly because your body will just fail again. I think I read somewhere there are plans for NPCs that live in the DR permanently. If that was official and is still in the plans, any character who was absent for very long can still claim to have been lost in the DR.