This is incorrect. The contract says that they can indeed to legally force him to go through with the deal and price that he agreed to. If it turns out to be more than twice the current valuation of twitter, they should do this. But they probably won't
They wouldn't be suing him to make the courts force him to buy them.
They would be suing him for damages - loss to Twitter's reputation and stock market value as a result of Musk's shenanigans.
Which would be....very tough to prove, but I wouldn't say they DON'T have a case.
They'd probably have a duty to try.