There sure is a bunch of naysayers and negativity popping up in this thread. People need to cool their jets and be a little patient. At least until after the Telltale asset auction.
Hey Braggy McBragface. How about you brag yourself to the brag strip so you can brag race against other bragsters. Afterwards you can go home and dress up in brag, and admire yourself in the mirror.
When zombie spawns start to thin out, simply quit your game and reload it. The horde will restart like it was just beginning. Just keep doing that until the end of the horde. Time will not be affected, so eventually the horde will end. However, it will keep your zombie spawn numbers high.