Has any show with a similar theme survived more than one season? Jericho made it two seasons, but those weren't full seasons.
What I mean by the theme is something set in a reality very similar, but vastly different than ours. Present day Earth but something like a nuke or nukes going off. I wonder if this just strains the credibility too much for the typical Network TV viewer. It's not a reality based show (like your typical crime drama), yet it's not a flat-out Science Fiction show, either.
How long could you set a show in a "present-day but different" reality such as this and yet keep it close to "present day?" If you nuke 26 US cities and divide this country into 3 entities, by next year reality will look totally different than it does now. Same with Last Resort. Nuke Pakistan, invade China and have a rouge sub threatening everyone's sanity and, this time next season, our world will look vastly different geo-politically.
West Wing was able to do it but their reality, while different, wasn't that vastly different from ours. The typical viewer could squint and believe it took place in present day. Middle East troubles, home troubles, economy, politics, etc... Nothing vastly different like nuking Washington DC and setting up the new US Capitol in Philadelphia or anything.
Love the show but I agree the concept seems to fit better as a mini-series and not some full series you hope or expect to run 3, 4 or 5 seasons.