TWD Will continue, as Zero says, they don't exactly follow the graphic novels, except for some major large plot lines like the Wolves......... who are coming.
The companion series is just to expand upon the current series but elsewhere in the country.
I've had a chat with Kirkman and Jonathan Maberry who has also written about a ZA, and there are characters from TWD in Maberry's Rot and Ruin series as the two are going to collide at some point WOOT