This may have been posted before, but even Durkon didn't realize that Malack was an evil spirit driving around the body of the lizard-cleric from long ago. I think that Roy's remorse over Durkon being turned into a vampire and his probable lack of the proper knowledge skill (http://www.giantitp.com/comics/oots0052.html) means that he will stand for Durkula, thinking (or wanting to think) that it is still Durkon. Belkar is still talking to Roy, but I think he needs to be talking to Haley and Vaarsuvius. I expect some interesting tension between Roy and Haley once she gets suspicious and V should be joining in at some point. However, my guess is that Roy will be in denial until something obvious happens (Durkula dominating Belkar and getting away before being 'resurrected' or just revealing himself when he bring mayhem to Durkon's old Dwarven home).
As for the casting of control weather, my guess is that it will have no effect (or very limited), but just enough to get Durkula where he needs to go. I do think Thor has the upper hand on the weather, but I am sure hHel was expecting this, she may have a way to just get them to Durkula's destination.
As much as I want Durkon to get back on top, I am curious what Hel wants Durkula to accomplish. I am waiting to see her plans being revealed.