Should a person quit or wait to be fired from an increasingly intolerable job?

I have been employed with a large company for 26 years, and it has been a mildly satisfying career until recently. Since a new CEO took the helm, working conditions have degraded exponentially. Some changes were necessary. Others are arbitrary and designed to intimidate employees to the point of resignation. For example, I recently phoned to report in sick, and I had to argue for an hour and a half before they would show me unavailable. The actuarial value of my pension at this point is about $400,000. If I stay for six more years, that amount will double. I believe that the shareholders have a right to fire me if I don't toe the line. But I believe that management is violating my rights by blatantly circumventing my contract. (For example, time off depends on manpower available, but they've laid off 20% of the workforce.) So should I quit now -- or should I hang on and wait to be fired?