I kinda digged how the Knights of the Ebon Blade dealt with their undeath.
They're still very powerful and very dark, but nobody can argue that the Ebon blade aren't good guys (Even if their "good" is achieved by questionable methods.)
They realized that there really "isn't" a place for Undeath in Azeroth and that instead of creating more, like the Scourge did, they can use their curse for good.
I've toyed with the Idea of the Ebon Blade taking command of the Forsaken, but the trouble is trying to find a reason to make them remain Horde.
Perhaps not even take official command. I would lay out something like this;
5.3 (Should this happen, SoO will be 5.4), The Knights of the Ebon Blade strike at the Forsaken, finally deciding that they won't let them become even more like the Scourge. (The Forsaken have to do something "really" big, first, something nobody can argue was good for anybody.) The Ebon Blade would strike secretly, as to avoid major conflict with the Horde, at first.
The dailies would consist of destroying plague-canisters and platoons of deathguards. The raid would start with your group and Thassarian taking out Sylvanas' chain of command, all the way up to Koltiria, at that point you beat him (Brainwashed at this point) to his senses, then They go their merry way. At this point, Darion would move in for the "Val'kyr" fight as well as the Sylvanas fight. He would make some sort of speech about how he will not allow any group become like the Scourge.
At this point, The Ebon Blade takes some of their bretheren who happen to be Horde-races and distribute them into the Forsaken's leadership. From that point, the "new" Forsaken leaders would "swear" loyalty to the Horde and take off their Ebon tabard.
Now, what this would do would be to not only add new flavor to that patch, but also cause friction between the Forsaken and the Ebon Blade.. Questions will be asked like;
"What's going to happen to our military campaigns now that the Ebon Blade has installed puppet-leaders?" or "We need to rise up against the Ebon Blade's leadership over us, but who will be our leader now that Sylvanas has had true death?"
That could be an interesting theme for the Forsaken; A group who hates their oppresive leadership, but a group who has nobody better to lead them.
I imagine they'd stay with the Horde, it we be so they don't warrent unnecessary fighting than what's already been caused.
Sure, my idea may have holes (Possibly A LOT of holes.) But, at least it breathes life into an old faction, tones the "villain" meter with the Forsaken, and causes a pristine chance for more lore possibilities.