In due course, which means at the proper or appropriate time, can have several synonyms depending on the context. One could use "eventually", which suggests something will happen at an unspecified time in the future. "In time" is another phrase meaning after some time or eventually. In addition, "in the fullness of time" can be applied to situations that require patience or are complicated. "As time goes by" carries a similar connotation, but focuses more on the passing of time. In conclusion, there are several alternatives to "in due course" that can convey the same meaning depending on the situation.