I really like the idea of Lazarus being Abaddon, mainly because this does seem like something Abaddon would do. Especially when Lazarus says “we have more virtuous pursuits to attend to”, Abaddon would very much like to keep magic a thing in Tyria. The Elder Dragons would like to consume Tyria and its magic. That would make the dragons an enemy to Abaddon and would give him the conviction to oppose them, and further more make an alliance with the Commander(since the Commander has had a hand in laying to dragons down).
As for Abaddon being dead… perhaps the artifact that was switched out as an aspect of Lazarus, was actually one of Abaddon’s artifacts. In the Personal Story, we have a mission where we are going into a lost temple of Abaddon to thwart Shaitan’s minions from getting Abaddon’s relics. What if a piece of Abaddon survive in one of them?
Finally, I think Abaddon is one of the most interesting and misunderstood characters in the GW universe. While he was the villain in Nightfall, was he really evil, or was he just driven into madness by his prison. His actions in Nightfall made it seem as if we were just trying to keep him from breaking out. I’m not saying Abaddon is a saint either, but then again, is anyone character in this game infallible?(Heck, in Nightfall, we made an alliance with Palawa Joko in order to hunt Abaddon, which restored him to power and allowed him to now rule Elona. So, we that played through Nightfall are the reason Elona is a place of undeath lol)