I would say the way to do it is to make a more compelling, relevant story that supplants the target meme. Throw in some military and politics, and you can consider it eradicated, for practical purposes.
If the idea needs a critical mass to support its corresponding god, then you don't have to kill or convert everyone-- just the majority.
In Europe and the Middle East, people were polytheistic until a couple of monotheistic religions won the day through military conquest, politics (give up your gods and worship mine, and you can become part of the ruling class), and plain old persuasion.
There are some people in Europe who worship old pagan European gods, but a direct chain of connection to the original worshippers doesn't exist. For all of them, from the Egyptian, to the Greco-Roman, to the Norse and Germanic, at one point, all of their followers abandoned that practice, and adopted Christianity.
So, as long as you just need to keep below a certain threshold, a newer, more compelling idea might do the trick.
For a modern-day example of this, you can look at Santa Muerte:
Santa Muerte, or "Saint Death," is a Mexican folk religion that
combines traditional aspects of Catholicism with ancient Aztec
religiosity to form a new faith. As the patron saint of death, Santa
Muerte is a kind of spiritual protector for a growing legion of
Mexicans who feel unprotected by the state and cast aside by the
In Mexico, it has become the religion of choice for transgender, gay
and lesbian worshipers, prostitutes, felons and drug traffickers, as
well as little old ladies, police officers, doctors, nurses and
judges. Santa Muerte followers say that death plays no favorites. Rich
or poor, powerful or peasant, death comes for everyone.
To outsiders it may seem as though Santa Muerte devotees are
worshipping death. But by embracing death, Santa Muerte believers say
they are free to live their lives without fear or anxiety.
The "old gods" of the state (okay, the state isn't technically a god) and the Catholic church (with God, Jesus, Maria, and a whole cadre of human saints) just aren't up to the task of taking care of people in certain areas of modern-day Mexico. A New God is arising. Arguably, she's gaining a sort of critical mass. For her followers, she is the force who truly has power over their lives.