In every good story the world is ever-changing, just look at the world in Star Wars (I suppose we should say “galaxy”) at the end of Return of the Jedi, the world had changed completely. In Lord of the Rings, the world had changed throughout.
Your characters change the world
In a roleplaying game, we have the unique opportunity to do whatever we want, without limits, so it’s inevitable that our characters will change the world around them. Also it’s nice to see the consequences of their actions, good or bad. If they’ve saved the world, make sure you show people recognising them and thanking them.
Show how the world is changing
If your character is an inventor, or maybe discovered a new device that helped them to save the day, what happens when that device becomes readily available to more people? This is something I always thought the TV series Stargate SG1 did better than Star Trek. In Star Trek they discover aliens with amazing new technologies all the time, but it never got added t otheir own arsenal. But as SG1 progressed they got new weapons and new technologies which gave them more storytelling potential.
Remember, this is your world, and your characters can shape that world!
There are more links to articles about worldbuilding here.
Top image is by Rudy Rucker.