Impermanence plays a role in many of the most engaging games on the market. It adds a lot of interesting opportunities in games, but it can also frustrate and anger players who miss out on opportunities. However, sometimes it also allows players to customize their play experience and can create a more concise and meaningful narrative than having a messy jumble of content waiting to be played.
One important thing to consider when implementing impermanence is that it can feel like a robbery. If people only get one opportunity to enjoy an experience that they really want to see, but they miss it, they will feel like they missed anything. Implementing such systems is really only useful in such a situation as you can be absolutely certain that there is other content that is equally as meaningful as the content being rendered inaccessible.
Another thing to consider when adding impermanence is how it actually effects content. It’s not uncommon for a large RPG to include things that can be missed in any given playthrough, and not allow players to return back to the content they missed. If the game can be played through multiple times, either because it has sufficient content that the repeated experience is meaningful (i.e. a New Game Plus that has altered experiences), or because it is somewhat random, then there could be less of an impact. Short games have less to worry; if players want to go back and see something they missed they can without too much difficulty.
There’s a number of ways that are common for marking off content in a game. One is through a “choice” gate. This is when the player’s actions will mean that they only see certain content. So long as there are an equal number of choices and the choices make up a sufficient amount of the game content, it’s possible to implement a choice gate in a game with replayability so that players can enjoy each path so long as they choose a different way on each time going through the game.
There are also “time” gates, that kick in once the player has progressed past a certain point. Some time gates are “soft”, meaning that players have plenty of opportunity to avoid passing through the gate and can complete all the potentially inaccessible content before they do, while some are “hard” and don’t allow players to complete all the content on any given run of the game.
The two remaining types of gates are both “situational” gates that only occur in certain times. Some of these are “game state” gates that rely on certain conditions to be met in game; for instance, a quest might only be available for characters between level 7 and 12. “Extrinsic” gates rely on out-of-game circumstances to determine whether or not something is available; a special event may only be available for a week in December.
Some gates also have reversible impacts; players may have to sacrifice in-game progress, but they could then reach the content again, like old chapter-select systems permitted. In some cases a “gallery” may be available to go back and see content out of context, allowing total access to potentially missed content.
As a designer, impermanence can often make a much better game; it means that players have direction, motivation, and potentials to see things that aren’t normally available and have special emergent experiences. It allows you to put in content that only makes sense in certain contexts and provides more realistic opportunities for progression, but it can also result in many players experiencing only a fraction of the game’s content, so should be used with care.