That's not how things work here in the real world. The big company would show to the NLRB that internal discussions of closure began well before any unionization effort, they'd show financials explaining why the store's closing, etc. and the NLRB would happily side with the big guy.

All of these situations are always adjudicated by a government bureaucracy that's often more inclined to side with companies than workers, in this case the National Labor Relations Board (NLRB). So it would work in that case exactly like it worked in this case: workers start trying to unionize, company lets workers go, workers appeal to the NLRB, saying they were let go because of the unionization efforts, and the NLRB investigates.

If the company produces documentation showing other reasons for having let the workers go, the company wins. If they can't, the workers win. In this case, the workers were very clearly singled out because of their organization activity, and the company had no complaints at all about their performance before the organization activity started, so the ruling went in favor of the workers.

Instead of firing workers, if the company had closed the store and the USSC hadn't ruled poorly, it would work exactly the same way. If the company produces documentation showing that the store was losing money more than other stores that remain open, the company wins. If they can't, the workers win, and presumably in that case the company could choose to either re-open the store (since leases tend to be long-term) or move the employees to other stores. More likely is that after a few of these cases, companies would be less quick to close stores to stop collective activity.

In any case, it wouldn't be complicated or a new thing at all, and wouldn't be easy to fool by starting unionization action at an already-closing store.