1.He said he must leave early.他说他必须早点离开.
句意表明其实在说的时候,他还没有离开.
所以应该把must leave early 换成will have to（将不得不）leave early.
2.He said he would have to leave early.他说他将不得不早点离开.
而且,因为主句时态是一般过去时(said),所以宾语从句的will have to也得相应改成would have to了.