When I originally thought of the catch it was just that only his family could bypass the catch because of 'bloodline magic' and shared magical heritage.
I think in this case, then, the eradication of his entire family line would have far-reaching personal consequences, and his Catch would be replaced by some new susceptibility, depending on which metaphysical direction the table wanted to go. This could be:
- susceptibility to the person who went to the trouble of murdering that entire family (and a new Trouble to reflect the enemy pursuing him)
- switching the Refresh around and making it immunity ONLY to the person who went to the trouble of murdering that entire family (a la Harry Potter and his weird immunity to Voldemort's curses) for some sort of vengeance story arc - that should free up some points for some new powers
- susceptibility to Spirit magic, or spirits, or anything which can be justified as the force of his ancestral line trying to pull him beyond the walls of death to join them
- susceptibility to the element which this unspoken villain used to destroy the family line
This sort of story event - the murdering of one's entire family - can be the launching pad for a great number of story options.
But the general response with eliminating a finite Catch is simply to find a new Catch - maybe one worth more points.