The antonyms for the phrase "coming undone" are "being put together," "held together," "staying intact," "remaining secure," and "maintaining stability." These antonyms all suggest a sense of strength and security, as opposed to the vulnerability and instability implied by "coming undone." Being "put together" implies a sense of completeness and wholeness, while "staying intact" emphasizes resilience and durability. "Held together" suggests something being kept in a cohesive state, and "maintaining stability" implies continuity and balance. So, while "coming undone" may suggest things falling apart, the antonyms offer an alternative perspective of things staying strong and secure.