There are lots of ways MPs can leave Parliament that don't involve an election. The most obvious is resignation. The most final is dying.
Becoming a public servant (e.g. a teacher) is effective, so is being convicted of an offence punishable by two or more years; or of what the electoral act calls a 'corrupt practice' (what Jami-Lee Ross accused his leader of). There's more besides. The new 'Waka Jumping' law has added a new method for 'vacating' a seat.
But what happens once an MP is gone?
If the MP is a list MP they get replaced by the next wannabe MP on the party list. That's how National MP Nicola Willis replaced Steven Joyce. She was the next cab off the rank.
But if the departing MP is an electorate MP (as Mr Ross is), the process is more involved, and will lead to a by-election - a tiny election that occurs only in the electorate of the departing MP.
The Electoral Act says "If the Speaker is satisfied that the seat of a member elected to represent an electoral district has become vacant, the Speaker must, without delay, publish a notice of the vacancy and its cause in the Gazette."
The Gazette is an old-fashioned thing - an official newspaper for important notices. All sorts of things have to appear in the gazette which you can read here. Bankruptcies, appointments to public boards, even the new levy rated for the slaughter of pigs. If you ever have difficulty sleeping it's worth a read.
This is where a note from the Speaker, Trevor Mallard, is posted to say the MP has gone. Last time the formal note went up the day after the MP departed.
From there the Governor General has 21 days to "issue a writ" to the Electoral Commission (who run elections) requiring them "to make all necessary arrangements for the conduct of a by-election to fill the vacancy."
This gives the Electoral Commission warning to be ready to fire all cylinders the moment the writ is received. "Immediately" they have to publicly announce:
1. When the by-election will take place.
2. The deadline for candidate nominations.
3. Requirements for those nominations.
There's a decent interval between the departure and the by-election. When Phil Goff left Parliament on 11 October 2016 the by-election to replace him was held in the first week of December, nearly eight weeks later.
In the interval the National Party will be down one MP and lose an MP's worth of its share of questions in the House. It has also recently lost questions as a result of the Prime Minister downsizing her cabinet by two.
And over that same period there will be a sudden surge of attention on Cockle Bay, Flat Bush and the suburbs between them. So Botany should maybe brace itself for lots of pre-Christmas attention.