To your first hypothetical, the company sues the union, union leadership is subject to jail time, and the company can ask for an award that has to be paid out of union funds, which means it comes out of your check. See APA in 1999, and the New York Transit strike of 2005.

Now, ask yourself this: if the absence of a union under the RLA granted an employee group strike at will, then why the hell does any airline have a union? The overall answer is the courts have ruled that the lack of a union does not absolve employees from their responsibility to exhaust all avenues of bargaining and negotiation before self help. See ASI, Inc vs IBT in 2014.

As to what the consequences of the latter would be, I honestly don't know, but at a minimum you're out of a job. But since you work at a union carrier it's irrelevant to your current situation.

To your last question, does the company just fire 500 people today? Well, that first assumes you can actually get 500 people to go along with your plan, and do so quietly enough that the company doesn't get wind of it before hand. How likely is that? Not very.

But what you should really be asking yourself is what would you be able to accomplish that market forces aren't already doing?

Not much.