When a stock is halted, SEC Rule 15c2-11 requires that market makers are forbidden to trade the stock until the company finds a sponsoring market maker who will file a form 211 application to FINRA. From the SEC halt order...
By definition, if there is no Market Maker for a security, it trades on the grey market. However, it is possible for a sponsoring market maker to submit the form in a timely manner so that the security spends little to no time on the grey market. Usually, grey market securities have very light volume, however they can be traded. Most brokers will accommodate sale of grey market stocks but some of the major brokers will not allow you to buy them.
The Form 211 requires specific disclosures before the security can be traded again. The following link describes these disclosures in more detail...
Whether and how quickly COUV recovers depends on how well they can defend themselves against the questions which were raised by the SEC. We really don't have any clarity on exactly what the SEC is objecting to. Hopefully we'll get a better understanding of what's happening on Monday when we hear from COUV again. In the meantime, we should all take a deep breath and hope for the best. With any luck, the Carbon Ion merger will get back on track if COUV can provide good answers to the SEC questions.