[Q] What happens to my E visa/status when I sell my business or interest in the business?

From a USCIS examiner's perspective, your scenario will be governed by the below CFR provision:

(iii) Substantive changes . Prior Service approval must be obtained where there will be a substantive change in the terms or conditions of E status. In such cases, a treaty alien must file a new application on Form I-129 and E supplement, in accordance with the instructions on that form, requesting extension of stay in the United States. In support of an alien's Form I-129 application, the treaty alien must submit evidence of continued eligibility for E classification in the new capacity. Alternatively, the alien must obtain from a consular officer a visa reflecting the new terms and conditions and subsequently apply for admission at a port-of-entry. The Service will deem there to have been a substantive change necessitating the filing of a new Form I-129 application in cases where there has been a fundamental change in the employing entity's basic characteristics, such as a merger, acquisition, or sale of the division where the alien is employed.

The change contemplated in your scenario will be deemed a "substantive change". Note that it says "prior" Service approval must be obtained when there will be a substantive change, which means in the event you plan to sell your E-2 enterprise business, you should obtain a prior approval of I-129 amendment of the change. If you do not plan to continue E-2 status in by purchasing another business, you should change status to another nonimmigrant status such as B-1 or F-1 student status before you sell your E-2 enterprise business. I think that will be the way USCIS will decide.