Originally Posted by The Glyphstone
This, too. The Zerg don't need to actually win the battle, they just need to spread Creep out over the battlefield after they win or lose. Unless the Orks happen to have a brainstorm and use flamers to beat back the Creep (and roast their own dead in the process), anything left on the field will get re-absorbed and re-purposed.
Creep requires structures to promulgate it though, and so the zerg would need to go around the lines or manage to have the orks completely ignore their structures.
I guess really it depends upon the savviness of whatever is controlling the zerg on Tarsonis.
I guess this is the era before brood mothers but after Zerg Queens started getting more autonomy/control?