It has been a long time since an MP died in office, let alone one as young as Rod Donald. Off memory it has been 20 years since an MP died in office, with the last three being:
Bruce Barclay died in 1979, leading to Geoffrey Palmer entering Parliament
Frank Rogers of Onehunga died in 1980, replaced by Fred Gerbic
Basil Arthur died in 1985 with National’s Maurice McTigue winning Timaru in the by-election.