Q: What if I open the business and it begins failing, or I open a business and I lose control?
A: The inherent length of time one has to control an E-2 business would generally be the validity period of the E-2 visa, or the length of your E-2 stay or immigration status in the U.S., which expires at some point. To extend your current visa, get a new visa, or extend your E-2 stay without leaving the U.S. so that you can to continue to live in the U.S. in E-2 status, you have to re-prove many, if not all, of the original items. If you no longer own 50%, then you may not be able to prove that you can develop direct the E-2 enterprise. If you have sold the business and no longer own it, you are not going to be able to submit the most recent tax returns, perhaps, or show other proof of ownership.
The government has gotten more sophisticated in fraud prevention. Whenever you submit an application for an extension of E nonimmigrant status, it usually goes to various databases, or on different types of social media, and it does its own due diligence to make sure that if you say “I own a company that imports widgets from Thailand,” then such a business exists, and you are still the person running that named company in its databases.