Allende was president for about 3 years and committed suicide in office. Either it was a Russian style suicide of convenience or he was unfit anyway. So one cannot say if he would have gracefully given up his power or not. But, historically the odds are not so good.
Lumumba was assassinated 3 years into his presidency. So enough people disagreed with him evidently.
And Castro refused to relinquish office until he died of old age. Much like a king wouldn’t you say?
Socialism and communism are 2 different things. Just because some country hangs the word socialist in their name doesn’t mean that they are. North Korea comes to mind. And lip service it is. After the revolution and they have executed all the bougie people, the strongest leader consolidates their power and bans all opposition parties. And even anyone who might pose a serious threat is in danger of death or imprisonment. See: Lenin and Mao for the 2 biggest examples.
Soviet Russia fell into a straight up dictatorship and well, Communist China doesn’t even bother to hide that it isn’t anymore. And neither government allows for much in the way of opposition then and now.
The socialist countries I can think of, like the Nordic countries, allow for open political elections and other parties to exist and participate in government. And they gracefully share and relinquish power if they lose an election. And interestingly enough, they don’t feel the need to brag about their socialism either. They just are.