FACTBOX: What next in Zimbabwe's political crisis?

(Reuters) - Below are answers to some questions on Zimbabwe's political crisis after opposition leader Morgan Tsvangirai withdrew from the June 27 presidential run-off, saying violence by President Robert Mugabe's supporters meant it could not be fair.

WHAT HAPPENS NOW?

Zimbabwe's government says the run-off will proceed anyway, with Mugabe virtually guaranteed to win the contest. The 84-year-old Zimbabwean leader would then be sworn in for another five-year term.

Governing the country, however, could be tricky because the opposition won control of parliament in the March 29 general election. Mugabe's ruling party has challenged some of those results.

Tsvangirai beat Mugabe in the first round of voting, but according to official figures fell short of the outright majority needed to avoid a run-off.

WHAT IS THE IMPACT ON ZIMBABWE AND SOUTHERN AFRICA?

The prospects of reversing Zimbabwe's economic meltdown are slim without a change in government. Mugabe refuses to consider reforms and Western powers are unlikely to provide the billions of dollars in development aid needed to bail out the economy.

Zimbabwe's neighbors could be swamped with an even bigger influx of refugees.

An estimated three million Zimbabweans are in South Africa, where there are rising anti-immigrant feelings. More than 60 African migrants were killed in recent attacks by mobs there.

Investors keen to invest in Zimbabwe will sit on their wallets despite a widespread belief that the once-prosperous economy could bounce back quickly under a new government.

HOW WILL AFRICA AND THE WORLD REACT?

The 14-nation Southern African Development Community is under pressure to respond after several African leaders criticized Mugabe's handling of the run-off. SADC foreign ministers are likely to discuss the crisis in Luanda on Monday.

Britain is pushing for Mugabe's government to be declared illegitimate and wants broader sanctions against the Zimbabwean ruler and his top officials.

Britain is expected to have U.S. support when the matter comes before the U.N. Security Council and the United States has said Mugabe does not have legitimacy without a run-off.

Military intervention by SADC or the African Union is not seen as an option, however, especially as it is likely to face fierce opposition from South Africa, the regional political and economic powerhouse.

Sanctions on Zimbabwe, rather than its leaders, are also seen as unlikely because they would hurt ordinary people most.

WILL THERE BE MORE VIOLENCE?

Tsvangirai has sought refuge at the Dutch embassy and police raided his party's headquarters in Harare.

The MDC and trade unions could take to the streets to protest against Mugabe's government, but that would probably prompt a heavy backlash by well-equipped security forces. Tsvangirai and other MDC officials were beaten in an aborted March, 2007 rally.

COULD THERE STILL BE NEGOTIATIONS?

South African President Thabo Mbeki has urged the two sides to hold talks. South African media had reported Mbeki, who has mediated the Zimbabwe crisis for more than a year, favored the formation of a unity government. The idea has not taken off.

Tsvangirai has said he is ready to negotiate with Mugabe's ruling party, but only if political violence stopped.

HOW LONG WILL MUGABE STAY IN POWER?

Mugabe has said he wants to stay on until he is sure that it is impossible to reverse a land redistribution program that saw thousands of white-owned farms seized and given to poor blacks -- one of the policies blamed for Zimbabwe's collapse.

Some believe that victory in the election could allow him to bow out sooner rather than later, by departing from a position of strength in favor of a hand-picked successor, and with the opposition in disarray.

(Reporting by Harare and Johannesburg bureaux; Editing by Matthew Tostevin)