I don't understand why the creator's lifetime ever enters the picture. Nothing else works like that. Most property belongs to you until you explicitly transfer it, and if you die it goes to your heirs. Some things (like patents) expire at a fixed time.
As it stands, the copyright term for a work written by a 20-year-old author will likely be decades more than the copyright term for an identical work written by a 90-year-old author. How does that make any sense? Come up with a sensible fixed term and use that, done, end of story. If the creator outlives the term, so be it. If the creator dies immediately, his heirs can manage the property until it expires just like they would with anything else they inherit.
As it stands, the copyright term for a work written by a 20-year-old author will likely be decades more than the copyright term for an identical work written by a 90-year-old author. How does that make any sense? Come up with a sensible fixed term and use that, done, end of story. If the creator outlives the term, so be it. If the creator dies immediately, his heirs can manage the property until it expires just like they would with anything else they inherit.