if sabellian failed to control the Black Dragon flight, can he join by leading the netherwing dragonflight ?
The Netherwings already have leaders, namely Neltharaku and Karynaku. As Sabellian isn't a nether dragon, and the Netherwing have no real love for their sire who essentially abandoned them, it would be difficult if not impossible for Sabellian to ingratiate himself to them in order to take control of the flight.
"We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see." ― Tom Stoppard, Rosencrantz and Guildenstern are Dead
What Aucald said indeed.
While there is speculation that another flight or two might join the 'council' of dragonflights in Valdrakken, the Netherwing would at best be tolerating the Blacks.
However, I'd say there is room to explore (in flashbacks or other media) the time after the events of The Burning Crusade, showing Sabellian et al. helping the Netherwing and rebuilding trust.
Either way, I am very much looking forward to seeing the Netherwing again, both from a story perspective and just to see what they look like in modern graphics.
But your duty to Azeroth is not yet complete. More is demanded of you... a price the living cannot pay.
This is a signature of an ailing giant, boundless in pride, wit and strength.
Yet also as humble as health and humor permit.
Furthermore, I consider that Carthage Slam must be destroyed.
Guess I prefer the Devil I know. I'm not saying Wrathion is a beckon of righteousness... but he does make the hard calls... right or wrong he has the will to fight. So far we only have Sabellion's word that he's cleansed his flight in Outlands... I need proof. Telling us how he did it would go a long way.
Very real possibility.
I really hope we do learn more about Sabellian and how he allegedly cleansed himself and the Outland Black Dragons, the fact that nobody has asked him that extremely relevant question is a rather glaring omission
as for the Nether Drakes, would be great to see them again but they probably don't feel much allegiance to Azeroth or need to leave Outland