I hadn't realized that Eric McCormack was on Highlander! I usually associate him with Will & Grace or Perception. But having read the wiki entry, I can see why you'd think of a crossover. (Actually, it would be kind of interesting as a general idea if the travelers made a mistake and took over an immortal who had faked their death, not realizing that immortals exist. Maybe the immortal's mind might stick around too? The possession/mind control prompt? Or maybe the travelers would just be really confused.)

Nora and Josh definitely both have secrets, so blackmail is certainly possible. (Also, what happened to all of the werewolf wives? Surely they'd want to know about their husbands?)