I understood it the same way you did, ClusterRat, I think the location was a vital part of the plan, hence the difficulties with making it work in the now altered location.
IIRC there was also a note by Ludwig somewhere stating that he was willing to accept the fact that if this plan worked it would mean he would most likely be killed as well... I think that the point was that in helping to defeat the werewolf his soul would still be freed.
KyoshoBallard is right. The book that Grace finds in the Schloss Ritter library states that:
"A person who becomes a werewolf against his will . . . is not completely damned until he tastes of human blood. Once he does, his soul is eternally damned and nothing may redeem him. Even without tasting of human blood, however, as long as the taint [of cursed werewolf blood] lays on the immortal soul, it cannot enter into Heaven, and will remain chained to the mortal plane upon death."
Therefore, Ludwig's soul would only be free to go to heaven if the Black Wolf (his alpha) if Ludwig caused the Black Wolf's death. Because Ludwig died while Vonn Glower did not, Ludwig's tainted soul remained on earth to haunt/guide Grace.
What I want to know is whether Ludwig, in constructing his plan with Wagner, and in guiding Grace to Wagner's opera, played enough of a role in Von Glower's death to retroactively liberate his soul or if he's out of luck since he died while the werewolf blood curse was still upon his soul.