Unions work best for workers in places like the public sector where the employer is a government that literally cannot go out of business and where the state grants the union a monopoly so that other companies cannot enter the market and displace the union workers. Teachers, police, postal workers, firemen ... these are roles where no market competition is allowed and consumers are not given a chance to chose alternatives when service gets really bad. That's where a union is most beneficial to workers because they can extract a pound of flesh from the public and the public can't do anything about it.
But at a place like the New Yorker, where people can get news anywhere, and there are upstart competitors nipping at your heels, a union will just hasten the decline.
Now management will have to go through protracted union negotiations to make changes to the labor force at the company or to adjust roles and responsibilities.
I love the New Yorker. I hope enough rich urbanites are willing to pay a subscription to keep the magazine going even if times move on.