In an extreme case of post electoral unrest triggered by rigged election results is in Kenya:
At least 180,000 people have been displaced by unrest as the humanitarian crisis grows after last week's disputed election in Kenya, say UN officials.
I cannot think of a case where elections rigged by the incumbents resulted in anything positive. Even if it doesn't escalate to the level of violence we see in Kenya today, there is at least apathy and distrust among the citizens.
There are cases where the incumbent force loses due to electoral fraud such as the 2000 elections in the US when the elections were subject to seemingly legalized rigging (scores of African Americans were not allowed to vote in Florida and then to add insult to the injury, the Supreme Court gave the presidency to G. W. Bush).