Here's the deal on that...
In DMW after Immo has been killed, ANY Lock with the "Imp in a Jar" (second one, not first one) and the parchment can initiate the ritual. From there, anyone with the Black Lodestone and a Soul Shard can reset the Nodes...
The only place the quest comes into play here is that you have the final Quest "Summoning the Dreadsteed" so that you can talk to the horse at the end and get the quest.
You MUST do every quest that leads up to "Summoning the Dreadsteed" or when you talk to the Pony it will only say "The Steed pulses with powerful Hatred" or something like that.