Hastings District Council chief executive Ross McLeod said if that eventuated, notice would be given to the electoral officer, from which point in time there would be a window of 89 days within which to hold a byelection.
From there it would go through the normal election process, with the deputy mayor stepping in until the election was held, he said.
If a councillor were to stand for and be successfully voted in as mayor, he said the council would be faced with another byelection, albeit on a smaller scale.
Chief electoral officer for electionz.com Warwick Lampp said the cost of a mayoral byelection, based on about 50,000 electors in the Hastings district, could be up to $100,000.
This would include expenses such as public notices, voting papers, postage, insurance and counting the votes.
"It would probably be no more than $100,000, maybe around $80,000 to $90,000," he said.
Another byelection to fill any vacant councillor seat, if a current councillor were to successfully run for mayor, would cost about the same if they were an at-large councillor, or less if they were a ward councillor, depending on the number of voters in the ward, Mr Lampp said.
As of yesterday it was understood that the National Party had received four nominations for the Tukituki seat that was vacated by incumbent MP Craig Foss in December - leaving the candidacy open for the first time since the early 2000s.
Although Tukituki electorate chairman Kevin Trerise could not divulge the names of the nominees he said they were a "good, broad cross-section" of the community, coming from a range of backgrounds including business and local government.
He said he was "absolutely" pleased with the calibre of the nominees, adding any of them could win the support of Tukituki party members.
Tukituki was a "strong National seat", which Mr Trerise said he was sure "any one of them [nominees] could retain".
Once the pre-selection process has begun, nominees cannot discuss whether they have put their names forward.
There was speculation that Hastings District councillor and unsuccessful mayoral candidate Adrienne Pierce had also put her name forward.
When spoken to last week she had not decided if she would stand. Yesterday she said she was "not, not-commenting" but could not speak with Hawke's Bay Today.
Hastings resident and former Air Force pilot David Elliott also said he could not comment on speculation he had put his name forward, however sources close to him confirmed he had.
The pre-selection process for the candidacy has now begun.
The board of directors will consider the nominations - with nominees partaking in interviews, and meetings with local Tukituki National Party members - before successful
candidates go through to the selection phase.
Electorate members would then choose delegates who would vote for their preferred candidate at a final selection meeting towards the end of February. It was hoped a final decision would be announced before the end of next month.
Mr Trerise noted the process was just beginning, and the party should be left to "quietly get on with its selection process".
Once the candidate had been selected, it would be "all go".
