It depends on the state's law, but as a general rule, the elector is replaced by a new elector supporting the same candidates. For example, Sec. 192.007 of the Texas Election Code allows the remaining electors to appoint a replacement elector by means of a majority vote:
- (a) The electors meeting to vote for president and vice-president may appoint a replacement elector by a majority vote of the qualified
electors present if:
- the vacancy occurred before presidential election day and a replacement was not chosen under Section 192.004 (Elector Candidate
- on or after presidential election day, an elector is declared ineligible or dies; or
- the vacancy is declared under Section 192.006 (Meeting of Electors)(c).
- (b) The chair of the electors shall notify the secretary of state of the name and residence address of a replacement elector immediately
on the replacement’s appointment.
This appears to be the most common approach, and is followed by states such as Alaska, California, Colorado & Connecticut.
In Florida, FL Stat § 103.021 (5) allows the state's governor to appoint another elector who swears an oath to support the same candidates as the deceased elector:
(5) When for any reason a person nominated or elected as a
presidential elector is unable to serve because of death, incapacity,
or otherwise, the Governor may appoint a person to fill such vacancy
who possesses the qualifications required for the elector to have been
nominated in the first instance. Such person shall file with the
Governor an oath that he or she will support the same candidates for
President and Vice President that the person who is unable to serve
was committed to support.
In New Mexico, the governor also fills the vacancy, picking from a list of names provided by the state chairman of the deceased elector's party.