It might not be the final nail in the coffin for the park as a park, but maybe as a company. That could even be good news.
After all, Lightwater Valley is an established destination for many (they get half a million visitors annually), the necessary infrastructure to operate a park is up and running on site, there are attractions there with many years left in them, and local regulations presumably allow a few more to be built without too much hassle. Even if the company is struggling, there's still an amusement park with potential there.
The million quid question is: how much potential? Or rather, is it possible to profitably operate a park on the Lightwater Valley site, even taking into account the capital cost of attractions? If so, what would it take to get there? It could be that a new attraction or two could turn the place around. Make it a regional destination. Pull in enough cash to build new rides at a rate matching the retirement rate of existing rides. Maybe even expand its lineup. That all that's needed is a little capital. If the current owners can't raise capital because they're swamped in debt and can't borrow any further, they won't get there. But if they go bankrupt, loans are restructured and a new owner with a better credit rating comes in, they might be able to raise that necessary capital.
Looking at the map, it seems like the only realistic alternative use for the site is farming. And to put it like that, there seems to be some rather stiff competition for that particular venture in the area. It would be a waste to tear down the park, because that same acreage of farmland probably won't make any more money. Selling the land for industry or housing looks unlikely too. Even if the demand was there, there's millions of other places nearby where a residential district could be built without needing to tear down an amusement park first. Whoever ends up owning the place would probably find it more profitable to continue operating the park, than finding something else to do with the site. Heck, at the map it looks like half the park is being farmed already.
I think the Ultimate could yet be safe for several more years. But it could also be that the park simply isn't viable in today's climate, in which case it may pack up and leave. Ex-parks like Camelot and American Adventure were abandoned without the site being reused for anything (I mean, if operating a park isn't financially viable, by default, as the owner you'd be better off not operating a park) and I daresay they were in slightly more promising locations as well. In the end, who knows, this could swing both ways.