Originally Posted by Sergorn 
Would it really be stupid though ?
I mean, Risen could already pass for a loose sequel to the Gothic games as it is.
-Sergorn
When they have Gothic back they own 2 reasonably strong RPG brands. Merging them into one wouldn't make much sense. Two brands allows them to alternate between the two, or slowly cooking one game while the other is in full production, and it gives more safety in case one brand dies.
edit:
I just remembered that Deep Silver / Koch Media owns Risen. Another good reason to keep things separated.