I think so. But as for the pilots, it won't matter. They won't open the cockpit door. They may end up landing a plane full of dead bodies, but at least there won't be anyone dead on the ground.
Yes, it will be. The reason "human wave" attacks ended was because humans invented machine guns. Otherwise, they work. Sure, you take casualties, but when you have more than 10 people to one enemy, they lose unless they have a machine gun with sufficient rounds. And that's not going to happen now. You simply cannot conceal a machine gun or machine pistol with 200+ rounds with current technology. Add in the close quarters of an aircraft, and you can forget about it ever again.
Even if the passengers fail because someone somehow did the impossible and got a machine gun on the plane, they will buy enough time for the pilots to get to a lower altitude or out over the ocean. That way, if the hijackers have some way to get into the cockpit, the pilots can auger-in the plane where it won't hurt anyone, and *nobody* will be using that plane to attack people.
Would the price in lives to thwart such a hijacking be high? Sure. But the American flying populace has demonstrated repeatedly, and just now in the citation above, that they are willing to pay it in order to protect those on the ground.