Joe Grundfest is a former federal securities regulator who’s now a professor at Stanford University. Even just for breaking off the deal, Musk could be on the hook for a $1 billion penalty or even more. For Twitter, the stakes are higher, and that’s why it may go as far as suing its unwilling buyer to get the deal done. The company has struggled to turn a profit and attract more users and advertising dollars. Its share price has fallen sharply, and investors are counting on the $54.20 a share Musk promised to pay. Now a protracted legal battle seems inevitable, says Grundfest.