As said above, people leave a game because they're not having fun playing the game any more.
If they're not having any fun but they think that the changes will make the game better, then whether or not there's a timeline or a roadmap... they'll tend to leave or at least stop paying - and come back when the changes are in place. Or if they're particularly unhappy with one of their characters, they'll play other characters in the meantime. Or some drop back to playing freebie accounts until the changes hit.
If people are enjoying a game enough to continue playing, then they tend to stick around anyway. The timeline isn't going to make a great deal of difference to them.
The populations now may be less than in previous examples... but people were talking about falling populations before most of the major change patches over the years. We've been here before. We've also seen threads like these before most major changes, where people talk about quitting because of not having ETAs etc... but those people always seem to stick around and populations don't really drop much before major changes and tend to recover pretty well after the changes hit.
AO has had a falling population for some time now - perhaps more because some of the major issues in the game weren't being addressed and perhaps because the game was becoming stale to some extent. Whatever the reason, the announcement of real change in the public domain and GFX improvements are more likely to pull people into the game than to push them away - whether or not there's a deadline.
It looks like we'll have to disagree... but history is certainly more on my side than yours.
X