1 Oct 2015 An investor can also earn substantial returns if the shares of the acquiring return (AAR) during the event window due to the announcement of M&A. However, the maximum number of completed M&A happened in the year What Happens to Stocks When Companies Merge?. Mergers are combinations involving at least two companies. The result of a merger could be the dissolution of one of the legacy companies and the During an acquisition, there is a short-term impact on the stock prices of both companies. Typically, the target company's stock rises, while the acquiring company's stock falls.