Yeah, Star Trek II will probably be a disaster. It's not Star Wars on TV, which is what many people want, nor is it classic Season 1-2 Star Trek. Nimoy is gone, Shatner might be disinterested (and getting too expensive).
So, what I think will happen, after one or two seasons of very low ratings, is that Roddenberry has successfully devalued the brand. It will exist in books and soon gaming, but Paramount will, as they attempted to in the early '70s, offer Roddenberry a deal and sell him the Star Trek franchise.
Now he owns the entire franchise fully. I don't know how that works with syndication rights, but he undoubtedly secured himself a paycheck because someone will want The Original Series airing throughout the 1980s. TOS was a bit of an odd syndication package, as it was less than 100 episodes, so it might actually get a boost from a one or two season Star Trek II if they're paired together.
Movies are unlikely. Roddenberry is financially secured, and may delve into novel-writing when his attempts at more TV pilots or movies fail. Once he passes around the early '90s, his wife inherits Star Trek. Like in real life, she might be able to pitch a reboot of this beloved 1960s classic for the popular syndication market of the mid-to-late '90s, and we will get a reboot then, fully owned and produced by the Roddenberry Estate.
*If* that is successful, that show might get a spin-off and maybe a movie or two in the 2000s. Hollywood has discovered that Nostalgia sells (again), and it's very likely that, like IRL, Trek will have some sort of reboot movie or continuation of the '60s show in the late 2000s or 2010s.