You can let missions linger for as long as you like, and even revisit them in the new game plus mode. The important thing to note is that no missions in ME2 disappear if left unfinished for a time. That means there's a few points at which control is wrested from you. You start out on a single path, then can branch out to a number of missions - then after all those missions are handled, it shrinks back to a single line again - before fanning back out. The structure of Mass Effect 2 is an hourglass shape, repeated. Mass Effect 2 Point of No Return explained

ME2 has a couple of them - and in a way how hard and important each point of no return is depends on what sort of Shepard you're playing. We've put together a separate page to answer the larger question of the optimum Mass Effect 2 mission order for the main and DLC quests, but beyond that, if you're going your own way, you should absolutely know about the point of no return. That naturally presents a classic worrying dilemma - that of finding the point of no return, the point at which the story takes that freedom off you and carries you along towards the end. Mass Effect 2 has an open-ended narrative that lets you take on most of its main story quests in any order you like - and while you're at it, the game is constantly throwing a slew of side content at you.

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