I’m sorry there’s been a tussle. Given their ages, I would strongly advise against reintroducing them. Boars trios need at least 1 square metre per piggy. However, that is not a guarantee that they will make it through their teens as an intact trio. You also don’t want to risk having three that all need to live alone.
It would be best to keep together the two that get on best. Either the two who are together now, or Jack with the other who wasn’t attacked. With any boar pairing you can only have one top pig.
Think about who seems to spend more time together then go forward from that. The single boar can live as a neighbour in the meantime, or you could try getting them bonded at a rescue. What you have to bear in mind is that it can be more difficult (but not entirely impossible) to bond a teenage boar. It may be suggested that you neuter them and bond with a sow (or three). If you go down that route, you have to think about your setup. Boars are best kept away from sow pheromones. Even if they can’t get to them, they can disrupt a bonded boar pair.
All the best deciding what to do next.