Is there a quest that marks the endgame, and if so, is it communicated to the player that the endgame is about to take place?
Furthermore, will it lock out certain secondary quests or make factions hostile to the player?
Can one continue playing after the main story line?
Best Answer
The point of no return is definitely a significant amount further than what kalina stated. The point where you're forced to start making factions hostile towards you is a quest called "Mass Fusion", where your actions during that quest will affect you. There are obviously points in the storyline where you can prematurely make a faction an enemy, but "Mass Fusion" is the point in the storyline where you're forced to make a faction an enemy in order to progress in the storyline. It is a very definitive point in the storyline where you can see the endgame approaching.