I'm not sure what the problem is here.
So they continued to have work available for two employees. I've been through company, not just department, closures where depending on the job people were doing, there were differing departure dates. I was kept on longer than most of the employees because I had to shut down the benefit plans, take care of the personnel files, notify former employees on COBRA of the closing of the plan, etc. There were finance people who were kept on beyond me because they had to take care of the severance checks, formally disband the company with the state, close out the various company accounts, and so on. That doesn't make the closure any less legitimate. If they had work for two employees for longer than they had it for the rest of the department and their departure date is still to come, that's still legal. If the were able to find jobs in different departments for two employees but not for everyone, that's still legal.
If you signed a release of liability, you're pretty much out of luck. But even if you didn't, there is nothing inherently illegal about having differing departure dates for different employees, or even about reassigning some employees and not others.