We don't have a formal date on which the Guild of Venturers ceased to operate. Tar-Aldarion was their founder and patron, and so they likely persisted through his reign as King of Númenor, which ended in II 1075. His successor, QueenTar-Ancalimë, reversed many of her father's policies, especially those regarding contact with Middle-earth. If the Venturers didn't come to an end with her accession, they would have lost a great deal of influence, and they're never mentioned again after Tar-Aldarion's time.