I've spoken with ckknight about the issue, and he said to keep the repository open:
if someone wants to make it work without Ace2, go for it or have it so that something better comes out so people use it instead of Dewdrop. preventing something being fixed feels like bad governance
Yes, Dewdrop will pull all of Ace2 down for someone running disembedded. If Ace2 is broken, however, Dewdrop will most likely be shunned and authors will either go away from it or actually do something about its Ace2-dependence.
Killing would mean officially announcing its death, what people do with its corpse is not our business then!
But like Torhal said, just don't worry about it anymore. If it breaks, it breaks. The project page gets a note that its EOL and not going to be fixed.
The repository is already locked, so there's no danger of someone trying to provide life support...
My thinking is that it's well overdue. Ace3 has been in widespread - hell, mainstream - use for at least two years now, and it was always intended to replace Ace2. The fact that people are still asking about (and making new AddOns for) Ace2 is incomprehensible, and the authors who just haven't gotten around to updating their Ace2 AddOns after two-plus years need to get on the ball.