The C-levels just need to look at stock performance and profit to see there's a problem. There is nothing that a director level person should be able to say to a C-level to make them feel comfortable.
Stock performance is a not a very good indicator, as it reflects emotion more than anything else. Profits and profit-margin, OTOH, are ones to keep an eye on all the time - whatever they do, you better know why they are doing it. If you lose control of both, you shouldn't wait for the chairman to fire you - help the board find a replacement and get out.