Also notice that addon authors move on. It's a game and a voluntary activity.
It just happens to be patch day when it becomes apparent, because things didn't get updated and hence start breaking.
In those cases either someone cares and picks it up, or users can look for a replacement. So yes, this is also the time to check if perhaps addon Y also serves the need that addon X (now in trouble) used to serve.
I thought the idea was to have it demise when Cata launches (because people update addons then anyway) and give it this grace-period that needs that become uncovered can be covered by ace2-free replacements.
Dewdrop is of course on of the more frequent reasons why addons are still ace2, that otherwise could easily be ace3.
I have only one addon that uses Ace2 and it's Baggins. For me it is irreplaceable (in the sense that there is no alternative out there that I could tolerate) and I have a personal Ace3 port (without a working config UI) that I can use if Ace2 dies.
Main roadblock of saving its config UI is of course Dewdrop. But the real solution would be a rewrite of the config UI into something more contemporary, but I don't really have the required cycles to do that myself, that and given that Baggins isn't my addon to begin with.
In any case, I can live fine with Ace2 dying. I think the disruption should be very manageable at this point.