Guardian should appoint another Branch...

As to the appointment of a successor, the Master had stated in His Will and Testament that should the ‘first-born’ of the Guardian not inherit his spiritual qualities, he should appoint another Ghusn (Branch). The word Ghusn has been used by Bahá’u'lláh to signify His male descendants exclusively. ‘Abdu’l-Bahá was designated as Ghusn-i-A’zam (The Most Great Branch) and Shoghi Effendi as Ghusn-i-Mumtaz (The Chosen Branch). Shoghi Effendi was not in a position to appoint a successor to himself because he had no son and there was not a single Ghusn who was faithful to the Cause of God. Every one of the descendants of ‘Abdu’l-Bahá had been declared a Covenant-breaker.

The Covenant of Baha'u'llah, p. 378, Adib Taherzdeh