On this page of our guide to Doom Eternal we answer the question if there is a Point of No Return in the game, beyond which it is no longer possible to return to the Fortress of Doom. From our description you will also find out if you can continue playing Doom Eternal after you have completed the main story campaign.
The story campaign in Doom Eternal is designed in such a way that after completing a particular mission you usually return to the Fortress of Doom which is the main hub of the game. During your stay in the Fortress you can prepare for the next mission, choose to repeat one of the previous levels, practice your combat skills against demons (in prison) or use the Sentinel Batteries to open additional rooms that contain some secrets.
Doom Eternal has a so-called point of no return. You will discover it when you return to the Fortress of Doom after completing mission 9 (Taras Nabad) and before starting mission 10 (Nekravol). The game will display an appropriate warning. Missions 10-13 must be completed without returning to the Fortress of Doom. They are launched consecutively.
Luckily, you will return to Fortress of Doom after you complete the last mission. Then, you can continue playing the game. You can resume your Fortress exploration to find more collectibles, and you can repeat any level at will in order to acquire missed secrets, to take part in additional battles, or to develop your character. You don't have to be afraid if you have missed something. All game attractions will still be available.