Traditionally eliminations occur during a barf bag ceremonies. This is where Chris will hand out a barf bag to the contestants who are safe, and whoever doesn't receive one is eliminated. Sometimes, no awards are handed out to anyone at all. Generally, elimination ceremonies happen after nightfall.
According to Chris, once a contestant walks the Drop of Shame in Total Drama Island,they can never come back, "ever." Also contestants can leave in sudden-death eliminations. Contestants may willingly quit the competition despite their teams winning, there being no elimination, or someone else on their team getting voted off.