What was the consequence of the "Allahabad High Court's judgment" on Indira Gandhi's status as a Member of Parliament (MP)?

She had to contest a new election within six months to retain her MP status.

Answer: She had to contest a new election within six months to retain her MP status.
The Allahabad High Court's judgment required Indira Gandhi to contest a new election within six months to maintain her status as an MP.

(She could remain an MP, but she could not take part in Lok Sabha proceedings was the decision of the Supreme Court).

On 12 June 1975, Justice Jagmohan Lal Sinha of the Allahabad High Court passed a judgment declaring Indira Gandhi’s election to the Lok Sabha invalid. This order came on an election petition filed by Raj Narain, a socialist leader and a candidate who had contested against her in 1971. The petition challenged the election of Indira Gandhi on the ground that she had used the services of government servants in her election campaign. The judgment of the High Court meant that legally she was no more an MP and therefore, could not remain the Prime Minister unless she was once again elected as an MP within six months. On June 24, the Supreme Court granted her a partial stay on the High Court order – till her appeal was decided, she could remain an MP but could not take part in the proceedings of the Lok Sabha.