Some of the things that have been mentioned earlier in the series relate to long term playability of a campaign. In part 8 I mentioned the idea of campaign resets, and how I don't like them (see the section in italics at the bottom).
Generally, the system proposed overcomes these issues by taking more powerful out of the day-to-day activities of a game (pulling their players into more administrative roles within the organisation), and ensuring powerful characters are never so far above the new players that they can't be threatened.
But, these ideas could dampen a player's motivation to keep playing. If a player has defined their play experience based on the growth of their character, what happens when this growth plateaus and their definition of play is no longer relevant.
The easy answer comes through secondary characters, and giving the player the opportunity to renew their pattern of growth with a new story.
That's a key part of the experience for me.
Here's a tangent...
If you go through movie news websites, there have been some recent articles about the shift in long-form movie narrative. Mostly due to Marvel's recent work. There are cries that "the sequel is dead, the movie universe is the new direction in film". Iron Man exists as a part of a wider continuity, other stories go on around him, and eventually he may be phased out of the films altogether (along with the core original avengers) to make room for a new generation of heroes.
Sometimes you've just got to learn to let go. Sometimes a character has told their story and it's time to move on.
Some players might not want to retire their characters within a wider game, once they become powerful figures within the narrative they might want to remain in that role.
A game system might apply a carrot or a stick at this point. The stick (penalty) for long term characters might come in the form of degradation, perhaps in the form of a rapidly compressed timeline for game events. Each game occurs on a fortnightly (or monthly) basis in the real world but represents an annual event in the game world, if we assume that characters start adventuring in their late teens, then after 20-30 games (around two years of game play) a character might start to lose physical abilities (one every second game thereafter), or may find regeneration after battle harder to succeed. This doesn't really work for the system currently in development, because it has a "real-time" downtime element for gathering resources/money and crafting goods. Another option might include increased chances of character death when a figure reaches a certain degree of prominence in the setting...better known characters have a higher price on their head and more assassins willing to take on that job.
A carrot (reward) might be a better approach. Maybe a player can voluntarily retire their character as an NPC, or sacrifice the character as a plot device. This would probably incorporate the Destiny Points mentioned in earlier posts. If a transition to NPC occurs, the player might "cash in" experience points invested into the character, maybe gaining 5% of the character's total experience as destiny points (round down)...the player would still get the chance to portray this character if the NPC is required for later storylines, but this character would only appear once or twice a year and wouldn't develop any further. If the player instead chooses to sacrifice their character for a wider story element, they might reclaim 10% of the character's total experience as destiny points, but this would have to be negotiated with event organisers. A player couldn't simply lose their character in battle then say..."Oh, that was a sacrifice, can I have my points now?"
A few more ideas using Destiny Points as a link between in-game narrative and out-of-game responsibilities will come in later posts.