After this, nothing is known of Jack's fate. It's likely that either he and his group escaped on another boat or that they were overrun by the zombies.
Since Jack's exact fate is not known to people even on the wiki, it was probably intentionally left a mystery in case he was to be brought back in a later game. There is no evidence so far that suggests another Last Stand game will be made any time soon, if at all, so we may have seen the last of Jack, but that does not mean he was killed in Union City.
