The only way the US government and financial sectors would be able to stop Boeing from going under after another crash, would be to so heavily subsidise its products, that airlines have no choice but to buy them. Boeing would then be effectively a state-aided nationalised company in all but name.
Well, to be honest that is not too far off of the current situation. $8.7 billion in tax subsidies from Washington state alone (
after removing their headquarters to another state), which of course pales compared to the $27 billion they get in revenues from defense contracts, and that is nothing compared to
$64 billion in federal loans and loan guarantees. Don't fear for the survival of Boeing, commercial aviation accounts for somewhat more than half of their revenue but they could dump the commercial division and still have a pretty nice company by anybody's standards.