If Mr Seymour did not get elected it would be curtains for the party but if he got in and was alone for three years, and wasn't leader "It might well be curtains, just a really slow curtains and that would be painful."
When you were alone and just one person in Parliament, it was almost impossible to sustain a party.
"David would be effectively an independent member for Epsom."
Dr Whyte made his comments in the latest of the Herald's Hot Seat video interviews of party leaders by a panel including NewstalkZB host Rachel Smalley and Herald columnists Fran O'Sullivan and Toby Manhire.
Dr Whyte said that when the news broke that Christine Rankin was standing in Epsom "poor David had a moment but he got over it very rapidly".
Christine Rankin was a name people recognised "but I think the more people discover, the less she will appeal".
People got the wrong idea about Epsom, thinking it was an older electorate of "Remuera duchesses".
But it was a very young electorate and Mr Seymour had more natural appeal to them.
Act shrank to just one MP at the last election - former Auckland City Mayor and National Cabinet minister John Banks, who assumed the leadership from Don Brash.
Prime Minister John Key has already give National Party supporters in Epsom his blessing for them to vote for Mr Seymour.
Dr Whyte said if the party did not get sufficient party votes to elect him to Parliament, he would feel a strong urge to offer his resignation.
He acknowledged in the interview that the electoral accommodation with National weakened the party's bargaining position.
But he said it was already weakened because of the certainty that Act would never support Labour in a confidence and supply agreement.
The series so far:
Thursday - Hone Harawira and Laila Harre, Internet-Mana
Friday - Colin Craig, Conservatives
Monday - United Future leader Peter Dunne
