I don’t know if either Ellison or the production bible ever got as far as figuring out how the series could end, but I think I know the perfect ending:The long-lost Control Room isn’t aboard the main ship at all; it’s on a small pilot ship preceding the ark by thousands of miles. To gain access to it the inhabitants of the ark have to rediscover the technology to fly a pilot in a shuttle out to the control ship. The moral being that the quest to do so becomes an analogy to the original goal of saving mankind through spaceflight.
Not officially. But bootlegs are available.