Failure or refusal to qualify – death, resignation or revocation of letters – non-designation.) Unless otherwise provided by the will, (a) if one of several executors named in the will fails or refuses to qualify and accept the office, letters testamentary shall be issued to the executor who qualifies and accepts the office, (b) if one of several executors to whom letters have been issued dies or resigns or his letters are revoked, the remaining executor shall continue to administer the estate, and (c) in either event the remaining executor has all powers vested in all the executors named in the will. If no executor is named in the will or the named executor fails or refuses to qualify and accept the office or, if after letters are issued the sole executor or all the named executors die or resign or their letters are revoked, letters of administration with the will annexed shall be issued in accordance with the preferences in Section 9-3 upon petition under Section 6-2 and notice as provided in Section 9-5.