Settlement talks between lawyers representing Redstone and former girlfriend Manuela Herzer, who filed the lawsuit last November, have broken down over the past 48 hours and litigation has "resumed," according to the Herzer court filing.
Trial is scheduled to begin on May 6.
Redstone's lawyers argued in a separate filing that he should not have to endure an invasive deposition in order to preserve his right to be heard at trial. A serious speech impediment limits Redstone's ability to testify orally, but he could present testimony "in another form," they said.
A trial could cause further embarrassment for the ailing Redstone and his family, and act as a continued distraction for media company Viacom Inc, which is majority-owned by the 92-year-old multi-billionaire.
In her lawsuit, Herzer is challenging her removal last year as Redstone's healthcare agent in favor of Viacom Chief Executive Philippe Dauman, saying Redstone was not mentally competent to make that decision.
She declared in the suit that Redstone was a "living ghost." Redstone's attorneys argued he was fully aware of his actions. Herzer had been set to inherit $70 million before Redstone changed his estate plan in October, according to court documents.
A Los Angeles judge previously rejected Herzer's request to depose Redstone, and instead allowed a psychiatrist she hired to conduct a brief examination.
Redstone's lawyers have told Herzer's side that Redstone plans to testify, said Herzer's attorneys, who added that should clear the way for his deposition. Redstone's lawyers have said they may ask that Redstone have his testimony taken at home instead of in open court, Herzer's lawyers said in the filing.