I bought all the DLC even though I didn't want to, so it is possible.
You don't need to buy all the DLC to finish the story. If that's what you're asking. You did technically destroy the Reapers and complete the game. I have a different take on IT than everyone else though. I don't think it was a dream, nor that the game is "unfinished" because Shepard has yet to defeat the Reapers.
Mine is more like.
-Ending is a Reaper-constructed virtual world using Shepard's memories (see Geth Consensus).
-Any action during the ending will affect what happens in the real world.
-So shooting the tube does actually destroy the Reapers. I mean how else would you set off the Crucible, as a player? Shepard interacts with the world in a few ways. Shoots something, triggers an event, or cutscene. Pushes the "use" button (E) on the control ending. Or the dialogue wheel, which may activate a cutscene.
-Much like the Geth Consensus level, Shepard is seen "asleep" in the real world, while in the server part, he is moving around and doing things. Think Matrix.
They did kind of say that the reward for understanding the story is the better off you'll be with the ending. I'd say the high-EMS destroy ending where Shepard lives and destroys the Reapers, while saving the galaxy is pretty good to me. No, EDI and the Geth aren't dead. So there's nothing to worry about. I think she forgot to mention synthetic friends in that last tweet, but you get the idea. There's also a little hint, suggesting that everything post-Crucible firing may not have been what really happened.
To quote the codex: The Reapers resulting control over the limbic system, leaves the victim highly susceptible to their suggestions.
That is to suggest that all the weird stuff during the ending is essentially caused by the Reapers messing with your head somehow. I mean, they have the ability control people's minds. They could put all this weird stuff on the screen and have people freak out about it. Certainly would explain all the strangeness.