User blog comment:James12708/Possibility of a Mass Effect 4/@comment-5687135-20121031201025/@comment-4807396-20121222054258

The Codex [|explains] why blowing up relays and using relatvisic kill vehicles are not viable tactics against Reapers.

The Reapers winning in the Refusal ending is just the logical conclusion of what you're told repeatedly over the course of the game: the Reapers can't be beaten with conventional warfare; if they could, the galaxy wouldn't be desperately throwing resources at an untested Prothean superweapon. The fleets you gather during the game are, in the words of Admiral Hackett, "an armada for delivering the device when the Reapers are most vulnerable".

As for what happens in the aftermath of the endings, they don't really give us enough information to do anything other than speculate. Until BioWare weighs in on the subject, even the most plausible speculation is just that, speculation. And I'd imagine that if BioWare wanted to put another ending in, they'd have done it by now; the game is getting close to a year old.

By all means, you're welcome to speculate, just as we're welcome to point out holes in your theories. It's not worth getting butthurt over, at any rate.