The phrase "hadst go" is an archaic way of saying "had to go", which means someone needed to leave a place or situation. Synonyms for this phrase could include "needed to depart", "had to leave", "required to go", "had an obligation to exit", or "had a reason to leave". Other possible synonyms might include "had to depart", "required to depart", "needed to move on", or "had to bid farewell". Depending on the context in which the phrase is being used, some other relevant synonyms might be "had to retreat", "needed to escape", or "had to withdraw".