WARNING: Potential spoilers ahead. Expand at your own risk.
Well, I suppose there is. I never really got closure when I finished Wolfen. The world still felt alive and kicking. But it's taking me a while to "tune in" to what else is going on. Helena was sort of a prank novella I added to appease certain individuals who will not be named *cough* Mia *cough* But that wasn't meant to be the end of it. I had originally planned to do 3 novellas for Helena. Now I'm thinking I should just put them together into a full novel (which it will be). So you have that to look forward to.
As for more beyond that, again, I have ideas. I even started working on some of them. But it's a tightrope walk trying to get it just right. My concern is that I will end up retelling the original story (which I do not want) or ruining it by messing up something in the sequel. I do have a title, and I do have a full cast of some very, very interesting characters. I just need to give them a place to go and a reason to be there.
I guess if you made it here and found this page, you deserve a little treat. So, as an Easter Egg, I will reveal that the title of the sequel to Wolfen (if and when I get around to writing it to completion) will be Infensus.