James H. Burns writes…
It's possible this is Hollywood-urban legend, but it's in all of the TV Batman histories — and Adam West once confirmed it to me, personally — (Which might only mean, of course, as must always be taken into consideration when divining the lore of anything, that he had read the same stories…)
It's reported that just a few weeks after ABC cancelled the series, NBC called Twentieth-Century Fox, figuring that the show, weaker ratings or not, might be a nice fit for their 1968 Fall lineup. But the studio had already destroyed the sets and there was no way anyone wanted to pick up the tab for reconstruction…
Well then, NBC couldn't have wanted it very badly.
I have no first-hand info on what happened with Batman but these discussions are not uncommon, and their meaning is often inflated by those involved with the cancelled series. It takes a bit of the shame and failure out of the cancellation to say, "We almost got another year." What would be uncommon would be if NBC actually got to the point of making a genuine dollar offer.
My guess would be that what happened with Batman was that someone at NBC called Fox and said, if only to be sociable, "Just in case we have a hole to fill in our schedule, what would it run us for another season?" Fox already had 120 episodes of the show and was probably eager to get them into syndication so they could reap the benefit of past deficit-financing investments. Perhaps the sets had already been destroyed but as I recall, the Bat Cave was the biggie and it hadn't been too costly to build in the first place. I'd be more inclined to believe that even if there was some discussion, NBC wasn't all that serious about picking it up and Fox wasn't all that interested in keeping it going.