Antonyms for the phrase "brought on board" may include "left behind", "excluded", "eliminated", or "rejected". These terms imply a sense of exclusion or rejection, rather than welcoming into a group or organization. "Left behind" suggests that someone or something was not deemed important enough to be included, while "excluded" implies a deliberate decision to keep someone out. "Eliminated" suggests a removal or dismissal, and "rejected" implies a judgement of unworthiness. Overall, these antonyms reflect a sense of exclusion or rejection rather than inclusion and collaboration that "brought on board" implies.