When it exactly stopped to be an option?
When the international community started taking substance, I guess.
Whether Maidan was started/supported/controlled by outer forces, fact is that the people chose to overthrow the government, whether pushed badly or not.
The same is true for Crimean people, even if the results of the referendum were positively rigged, dont tell me that the people cheering in the streets of Crimea are mind-controlled and only represent the minority, and that people at Maidan were free men that represented the majority.
Maybe after everyone have conceded those 2 points (both coup/protest/revolt/whatever of Maidan and Simferopol are as illegitimate/legitimate/whatever as the other) we can start talking of more debatable topics.
The thing is, they are incomparable in nature. EuroMaidan ousted Yanukovich illegally, however this happened quite peacefully relative to this kind of event and what it usually causes. It was definitely not a coup and not a revolution either, as the parliament did not change.
Now, I believe the unilateral referendum in Crimea is legitimate if you completely forget about russian soldiers invading it beforehand for a completely warped up reason ("WMD in Irak"-style, should I add) and infecting the population of another country with russian propaganda.
So no, conceding that those two things are "as legitimate/illegitimate as each other" is not the start of a healthy debate. As I said before, just because one recognises two sides to an argument doesn't mean they are equal or that the truth is in between.