The antonyms for the phrase "was derelict" would depend on the context in which the phrase was used. Derelict typically means something that's been abandoned, neglected, or run-down. So, the antonyms for "was derelict" could be "well-maintained", "well-kept", "functional", "active", or "in-use". For example, if a building was described as derelict, the antonyms could be that it's been "carefully maintained" or "well-preserved". Similarly, if a person was derelict in their duties, the antonyms could be that they are "responsible", "diligent", or "dependable".