That's one of the problems with the Dark & Gritty approach. It always has to one-up itself.
That's true. The producers and writers on the series have said publicly they want the show to go on indefinitely. I'm not sure modern audiences will accept a story arc that has the characters forever living a more grim life. There has to be IMO at some point hope and a search for the "cure," or people will tire of new and existing characters simply getting killed off each and every season.