Curious question from a new comer. Welcome to PP forum. It is hard to answer without knowing your intent.
I've had my rib broken from martial arts once. I can not imagine trying to defend in a serious fight in that condition. It is hard to imagine that a person so injured, would start a fight. That was my first reading of your post.
Do you mean practicing with someone with a broken rib? I think a person practicing with a healing rib fracture, and I did, should avoid contact. For 6 weeks, you practice lightly and don't aggrevate the injury. That is a good time to watch training videos and maybe learn a new kata S-L-O-W-L-Y. Gradually you work your way up in intensity in solo practice where you can have control over the impact and avoid slowing down your healing with an unpredictable hit.
I realize this has less to do with pressure points, but it is the experience of someone who has had a broken rib.