Antonyms for "fills in for" can include phrases such as "misses out on," "leaves vacant," "does without," "neglects," or "ignores." These phrases imply that there is no replacement or substitute for the original person, task, or position. It could also indicate a lack of care or attention to the position that needs to be filled. In contrast to filling in for someone or something, these antonyms suggest a lack of action or involvement. In some situations, these antonyms can lead to negative consequences, such as missed opportunities or a lack of productivity.