Something inspired by the concept of the game SBURB featured in the webcomic that got ruined by its own fanbase and author; Homestuck
The idea of a group of online friends playing a game together, learning it overlaps with reality and will result in the destruction of their universe, with their only hope of having a home to complete the game and create a new universe to inhabit. These friends are then transported to their own "planets", based around their ideas of what an alien fantasy world they as an individual would have to save would be like, meanwhile having to rely on their friends for progress and resources, creating an inter-dependency while forcing them to become independent paradoxically.
Meanwhile, they are faced with enemies at every corner who do intend to destroy the world of the game, i.e. reality, and make it anew, seeing these "heroes" as the primary hurdle in their efforts while fighting the forces of "good" which are destined to lose.
As all this occurs, they have to come to terms and accept the distinction between their friends' online personas and their true selves, even meeting them in person, and what the resulting interactions entail.
To accomplish their goal, they must each visit the worlds of their friends, and face their inner demons personified in the form of an individual boss before joining each other in a final effort on the central battlefield their planets orbit and defeat the final boss.
In an ideal world, it would be a small group game, where each players gets to also be DM for one of the planets IC and OoC. For that reason and many more, it's been a difficult concept to pitch and convince people to play in.