What happens to the stock of a publicly traded company in chapter 11 if it is bought out by another company?

It can be two ways. If the other company is a publicly traded company, the shares of the acquired company would get merged with the acquiring company's shares. All shareholders of the acquired company would be issued new shares of the acquiring company at a ratio that would be defined during the acquisition. If the other company is not a publicly traded company, they may opt to retain the stocks in the market of buy them all from the investors at a predefined price that gets fixed during the acquisition.