Nadine Sierra has withdrawn from the Royal Opera House’s new production of “La bohème.” As a result, Simona Mihai and Joyce El-Khoury will replace her. First Romanian-born British soprano Simona Mihai will sing in performances scheduled between Sept. 11 and  Oct. 3 excluding the Sept. 23 performance. Then Lebanese-Canadian soprano El-Khoury will take over Sept. 23 and Oct. 6, 7, and 10. As originally scheduled Mihai will sing the role of Mimì {…}