Toshiba’s shares have slumped around 27 percent in Tokyo since April when the company first disclosed irregularities in its books. The independent committee is likely to say Toshiba needs a governance overhaul, and more than half of its board could be replaced at the next shareholders’ meeting in September, sources said on Wednesday. A Toshiba spokeswoman said the company had not yet made any decision on the matter and was waiting for the third-party committee to release its findings.