Elon Musk is warning Twitter employees to brace for “difficult times ahead” that might end with the collapse of the social media platform if they can’t find new ways of making money. Workers who survived last week’s mass layoffs are facing harsher work conditions and growing uncertainty about their ability to keep Twitter running safely as it continues to lose high-level leaders responsible for data privacy, cybersecurity and complying with regulations. Musk’s first companywide message to employees ordered them to stop working from home and show up in the office Thursday morning.