Glad I'm not the only one noting the Lost references. Makes perfect sense too, as Edward Kitsis and Adam Horowitz are referencing episodes they wrote.

The idea was that no one author should be writing the stories for them. So it did make sense from a character perspective for Henry to do so.

If the writers hadn't had Henry snap the pen in the finale, the series would be over. Henry would write everyone a happy ending and the series would be done. So it made sense that the writers concluded that story element the way they did.