The court may appoint a guardian for an unemancipated minor if all parental rights of custody have been terminated or suspended by circumstances or prior court order. A guardian appointed by will under Section 75-5-202, or by written instrument under Section 75-5-202.5, whose appointment has not been prevented or nullified under Section 75-5-203 has priority over any guardian who may be appointed by the court, but the court may proceed with an appointment upon a finding that the testamentary or instrumental guardian has failed to accept the testamentary appointment within 30 days after notice of the guardianship proceeding.