If push comes to shove.  You could always import it a a prop and replace it,  load the textures and inherit the bends.  If you are not going to animate it then you should be okay? Do you have Hexagon? or 3ds.    You could go back and regroup the model and reimport it that way? I have Zbrush but I am not sure hot to regroup it there?   Okay Go back into Zbrush, Go down about half way on the right there is the frame button. Click on that frame button it will show you the different groups by color.  Eliminate the neck that way by deleting the neck polygons. And then try to import it again that way. Now remember since you had the neck attached when you where in Zbrush if you streched the lower jaw or the neck muscles your model may or may not line up? One more thing is to make sure that when you where in Zbrush that you did not divided your model, Other wize when you go to import it,  It would not work any way because you changed the number of vertices that way. If you did that,  then I think there only two ways to save your model .  One way is to import it as a prop,  the other is to import the displacement map. Maybe some one out there has a better solution.. Good luck.....