I hear this a lot and I get it, but I'm not so sure it's true. If Boeing dies, their assets don't just evaporate with them. There are half a dozen companies in the US who could take over where they left off - hopefully with better leadership this time around.
Like who? Lockheed maybe? I'm not sure they'd be willing or able to take over without the US government stepping in with some serious incentives though.
Boeing and Lockheed Martin get a lot of name recognition for handling the high-level design and manufacturing of aircraft. But in reality, their planes are an amalgamation of engines, avionics, and interior systems which are often contracted out to other companies like those I listed. Many of them could step up and fill Boeing's shoes if a good deal presents itself - especially if there was extra incentive seeing as it would be a matter of national interest.
This is a strong argument to work with Boeing to correct both the engineering and company cultural issues that produced an aircraft that kills their customers' customers. What's happening now seems like the time elapsed in the penalty box for bad behavior and now they are back on the ice. As you've stated, Boeing is too important to go out of business. Should a crash happen in the western world they'll long for the difficulties and corrective opportunities they face now.