A fractured wisdom tooth is a tricky problem. If it is completely covered by the gums, you may take a chance not getting it extracted. However, on a professional level, I would need to tell
you that a fractured tooth
is a constant risk of infection
spreading through your jaws, even though it is not giving you trouble at present. No surgeon would take responsibility for that should it happen. You would have to take responsibility for the decision.
On the other hand, the tooth should be extracted if
1. It is partially or completely visible through the gums
2. Before fabrication of a complete denture, if it is the only tooth left.
3. If it is symptomatic.
Hope this helps.