Vostok Games' Survarium might console you. The team took many of the concepts that it was developing for the (now canceled) single-player Stalker 2 and decided to create a free-to-play MMOFPS out of it instead.
In an interesting interview with PC Gamer, Lead Designer Alexei Sytyanov paints a picture of "the green apocalypse" that hits the whole world, causing mutations and a ravaged ecosphere. Sytyanov says that players will need to band together to overcome the odds: "On top of the story and game tasks, there is communication and competition between the players, all to add dynamics and unexpectedness to the gameplay. Each game session differs from the previous one. The game constantly encourages players to show their inventiveness and skills, abilities of strategy to achieve victory."
From the sound of it, Survarium is a lobby-based MMO with timed sessions (Sytyanov says that these will go from 15 to 60 minutes based on the mode). Players can choose from PvP, co-op, or free play modes to explore the world, attempt to achieve objectives, and generally survive the best they can.
Even with the lobby structure, Sytyanov indicated that there will be player actions that will persist: "Ultimately, the side accomplishing more tasks will impact the story. Therefore, it will decide whether that story object is to get preserved or destroyed for the entire world of Survarium."