BioWare's official Facebook account recently made a vague statement about the ending of Mass Effect 3, and alluded that the game's ending was final, and that what players got with the game was what they had to stick with.
However, in the wake of more recent complaints and disappointment about the game's ending, BioWare has changed their stance, with a statement that its developers are "still collecting and considering" player feedback and have not yet made any decisions over requests to change the ending.
In other words, BioWare is currently performing damage control and may well change the ending if the pressure from fans keeps up. They are also taking suggestions on how a new ending might be implemented.
We are aware that there are concerns about a recent post from this account regarding the ending of the game. In this post it was stated that at this time we do not have plans to change the ending.
We would like to clarify that we are actively and seriously taking all player feedback into consideration and have ruled nothing out. At this time we are still collecting and considering your feedback and have not made a decision regarding requests to change the ending.
Your feedback and opinions are of the utmost importance to us. We apologize for any confusion this has caused. Our top priority regarding this discussion is to keep communication with you, our loyal fans, open and productive.
Should BioWare heed fan demands, Mass Effect 3 may well be first major title to feature a collaborative design between its developers and fans.