I think the general consensus showed by a lack of interest in The Alphas cliff-hanger shows why the series was canceled. As an unwanted public service (the easy kind to fulfill, meeting social obligations is no problem if you pick'em wisely
) I will tell you How It All Ends.
Dr. Lee Rosen is not killed. But he is very unhappy to discover that the reason Stanton Parrish had designated him the new leader was because, unbeknownst to him, Parrish knew that Rosen was one of his descendants. Rosen finds it really icky that one of his grandmothers cheated with Parrish, but, really, these things happen.
The photostimulator that created new Alphas is eventually reverse engineered to become a destimulator. Alphas who work for the government are the only Alphas left. The revolutionary threat posed by the power of "ordinary" people is repressed. This is just as it should be because human nature decrees that ordinary people are unfit for power. That is why every Alpha has some miserable weakness or flaw created by his or her ability.
Except that eventually Parrish will escape and find a cure for the destimulator! That is because human nature also decrees that the rabble will always have some class traitor who panders to their malevolent dreams of a world where they, instead of those who earned their privileges, have power. The end is not really an end, but an endless Manichean struggle, that corrupts the defenders of order and justice by the tragic fate of humanity at war with itself.
Or, to put it another way, angst never really dies, it just changes actors!