I don't think
Lost was "saved" by its end date at all. It was far better than the average show, even when it was "bad."
Heroes wouldn't be saved by an end date, either. The writers are just incompetent. Maybe an end date on their contracts, dated TODAY, would save the show? Better yet, use a time machine and date it END OF S1.
The X-Files wouldn't have been saved by an end date. The mythology was just a convoluted mess. A sooner end date might have obscured that fact, but not changed it.
ENT wouldn't have been saved by an end date. It had three years of pointless plotting, followed by a personnel change that finally allowed the fourth season to have the glimmerings of something worthwhile. It needed an extension of its end date. Like
Heroes, the problem was in the writing room, not in the length of the show.
ENT got better with the threat of cancellation, apparently.
ENT got better after it had been cancelled, and Manny Coto was brought in just to finish out the final season. Maybe having been written off was what allowed the show to finally get someone good in charge?
BSG wouldn't have been saved by an end date. Its premise was botched from the start. RDM et al needed to sit down and work out a better premise before they set the first pen to paper. (Still, they did pretty well, considering how they handicapped themselves from the start.)
Here's one that could benefit from an end date:
24. It's beyond repetitive. The final season should be announced as such, because then we can have the fun of wondering whether this is the day Jack finally dies.
I think, as soon as shows have one or two successful seasons, they should be given an end date, rather than maybe or maybe not getting picked up every year.
That will never happen. Any show with good enough ratings to survive will be renewed as much as possible. Networks can't afford to lose any shows that work, because most of what they try fails. Their few hits have to pay for their many failures - that's their business model.
It's very unusual for TV producers to have the clout (and the guts) to end their own show. How do
they know they'll ever have a successful show again? They're in a very iffy business and to cancel their own show might mean they're cancelling their own career. How many people here would walk out on their jobs, especially if they were in a profession where it was far from certain they'd ever get another?