Most, if not all of us know about what the original ending to Mass Effect 3 would have been thanks to a leak released sometime in 2011: an unstable fluctuation of Dark Energy was basically a century away from destroying the universe, and the Reapers were revealed to be THE ULTIMATE renegade faction that somehow had the power to combat this crisis by making new reapers out of sentient species.
Up until now, they have only been able to delay the implosion of the universe. No reaper at present is mighty enough to stop the build-up. Their plans were to assimilate the genetically-diverse (special) human race into a human-reaper (as they attempted to do in the Collector Base), which would then have the ability to use a completely different form of super-space magic to stop the cataclysmic event from happening and restore balance to the fabric of the universe.
All because humanity is far more unique than any species ever to exist in the billions of years the universe existed.
In the end, Shepard had the choice to allow the Reapers to harvest all of humanity, which would, in theory, put an end to the dark matter threat once and for all. If not, he/she could give Harbinger the royal finger, destroy the reapers and leave the universe to scramble for a solution and hope for the best.
Tali's recruitment mission in ME2 made strong reference to this ending, so it's not like it's a reaper trick to try and get humanity to submit.
So on that note, let's assume the reaper's word is kosher. This would be quite a shocking ending, to say the least. You don't just give your own life up like almost everyone was prepared to, you give up your entire species to stop the ultimate threat; and if you don't, perhaps the entire galaxy is doomed anyway.
Now, I know everyone is tired of hearing about the endings of Mass Effect 3 and I don't want to come across as beating a dead horse, but a point that crossed my mind: Based on the fact that many felt "space magic" was far too out-of-character for the series; the assumption that closure would still be lacking so everyone would be left to their imaginations and "discussions"; and the fact that there would have been no real option for a personal happy ending (no blue babies or a house on Rannoch). It seems (to me) like either ending, Dark Energy or Catalyst, would have ultimately relied on some form of space magic and that, given the above arguments against the current ending, the negative fan reactions would still be a large factor.
So I'll get to my additional point: Say the game shipped with this ending...
What the hello Bessy would we do?
I have been thinking about this topic for quite a while, and in truth, I don't know what I would have done of ME3 shipped with the original planned ending. The more I think about it, the more I honestly prefer the "new" ending over the original because, well, the choices aren't nearly as hard and black-and-white as the Dark Energy choices. (Don't get me wrong, I still believe the "new" one was rushed and underdeveloped and could have been much more satisfying, but let's not open that case file back up...)
So, faced with the annihilation of the entire universe, or just your own species, what would you have chosen, and why?
The answer isn't all that obvious.
If you wish to discuss another "what-if" scenario, you're welcome to visit my other post; Mass Effect 3: Off the Record