Death, etc. of Governor before oath of office
Section 181(1) · 1999 Constitution (2004 edition)
What Constitution says
(1) If a person duly elected as Governor dies before taking and subscribing the Oath of Allegiance and oath of office, or is unable for any reason whatsoever to be sworn in, the person elected with him as Deputy governor shall be sworn in as Governor and he shall nominate a new Deputy-Governor who shall be appointed by the Governor with the approval of a simple majority of the House of Assembly of the State.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 85. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections