It’s all up to Elizabeth Holmes.

Theranos, a blood-testing lab started and led by Ms. Holmes that promised to revolutionize the industry, is now under criminal investigation and faces increasing skepticism about whether its core technology works. Several federal agencies are looking into the company’s operations. Ms. Holmes herself may have to answer to federal regulators about what she told investors.

Just last year, Theranos was a Silicon Valley favorite with a $9 billion valuation. Now, depending on the outcome of the investigations, including the threat of crippling sanctions by the Centers for Medicare and Medicaid Services, the company could be forced out of business and Ms. Holmes could lose her position as chief executive.

The troubles have led to a cascade of questions about what changes Theranos might make to rebuild its reputation and business prospects. Some have even said that Ms. Holmes should step aside.

After more than six months of intense questions, though, changes have been limited. And whatever future moves the company makes are up to Ms. Holmes. She — not the investors, and not even the board — controls the switches.