Updated at 5:15 a.m. ET on Monday

A noon Monday deadline for President Robert Mugabe to voluntarily step down has come and gone with no word whether the longtime strongman of Zimbabwe will comply. Parliament has promised to initiate impeachment proceedings to remove him.

Mugabe's governing ZANU-PF party — long his personal fiefdom — showed how thoroughly the tide had turned by voting Sunday to remove him and appoint ousted Vice President Emmerson Mnangagwa as his replacement. The move marked a major turn in nearly four decades of the 93-year-old Mugabe's sometimes brutal and tyrannical rule.

But in an address broadcast on state television Sunday night, which some observers had predicted Mugabe would use to announce his resignation, a defiant Mugabe refused to fold, saying he will oversee a congress meeting in a few weeks.

"I will preside over its processes, which must not be prepossessed by any acts calculated to undermine it or to compromise the outcomes in the eyes of the public," Mugabe said.

Earlier Sunday, ZANU-PF said Mugabe had until midday Monday to step down and if he refused, that parliament would step in.

"If Mugabe is not gone by Tuesday, then as sure as the sun rises from the east, impeachment process will kick in," a member of opposition party MDC-T Innocent Gonese told The Associated Press.

In his Sunday night address, Mugabe said the way forward cannot be through "vying cliques that ride roughshod over party rules and procedures." Instead, he called for a return "to the guiding principles of our party as enshrined in its constitution."

Videos posted to social media on Sunday showed members of ZANU-PF breaking into cheers as well as song and dance, following their vote to oust the world's oldest head of state.

Tsvangirayi Mukwazhi / AP

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AP

And in a major show of unity one day earlier, thousands of Zimbabweans took to the streets of the capital, Harare, to demand that Mugabe go. The AP reports, the protest itself was a demonstration of just how much things have changed in Zimbabwe as the protesters would have faced a police crackdown just days earlier.

The ruling party also voted Sunday to dismiss Mugabe's unpopular wife Grace. "Without the military's intervention, first lady Grace Mugabe likely would have replaced Mnangagwa as vice president and been in a position to succeed her husband," The AP reports.

But questions abound about a Zimbabwe under the rule of Mnangagwa, a man who has earned the nickname of "The Crocodile." As NPR's Ofeibea Quist Arcton has reported:

"Emmerson Mnangagwa is no street angel. He is no savior. He's cut from the same cloth, the cloth that has seen Zimbabwe's economy tumble. This was the breadbasket of southern Africa. He's also seen as having been absolutely brutal in the '80s in Matabeleland when there was a massacre. So people shouldn't think of Emmerson Mnangagwa, who may come back and head an interim government, as being a savior for Zimbabwe - certainly not."

Mugabe has maintained an iron grip on power for 37 years after helping topple white minority rule in then-Rhodesia. His leadership, once regarded with hope of united independence, became characterized by a brutal crackdown on opposition, the seizure of white-owned properties and a crash in Zimbabwe's economy.

It was the firing of his deputy Mnangagwa two weeks earlier that precipitated his own downfall; the Zimbabwean army took over Wednesday, in what it described as a "bloodless correction."

Mugabe said Sunday that the army takeover was not "a challenge to my authority as head of state and government."

Sunday's vote by the central committee of ZANU-PF came from Mugabe's own party, "the party that for years was considered a bastion of (Mugabe's) regime, but has recently been riven with rivalry and infighting," reports NPR's Ofeibea Quist-Arcton from neighboring South Africa's city of Johannesburg.

On Sunday, the increasingly-isolated Mugabe met with the military leader who had placed him under house arrest. Aftwerward Mugabe said, "arising from today's meeting is a strong sense of collegiality and comradeship."

But as Ofeibea reports, Mugabe was "looking a little weary and sometimes losing his place," during the speech, even as he clings to his seat of power, for now.

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