None of the Forsaken know that Osan’gar (Corlan Dashiva) is dead, but they know he’s vanished. They are pretty much sure that Sammael is dead, because he isn’t the type to remain in hiding, but think Asmodean might well be hiding out until he can figure a way to return safely. They know that Rahvin and Be’lal are dead, though some at least suspect reincarnation as Aran’gar and Osan’gar. Most have worked out that Moridin is Ishamael.
Aran’gar and Osan’gar are Balthamel and Aginor transmigrated, respectively. Most of the Forsaken we’ve had in POV seem to have figured that out.
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