I think its fighters responsibility to report any injuries to UFC with confidentiality and no fears that their opponents will know about them.
That's why they should be reporting to Joe Silva, matchmaker, who can find a few options and report to the other side there is a slight chance your match made be change but keep training for your opponent.
Then you have a few fighters just watching on the sideline for any update but be ready to step up so we don't have a mess like UFC 149 or something rarely seen like UFC 151.
Sure these fighters on the sideline made not have a full camp or anything but they can figured out if they wants to fight or not.
Then you have the UFC deciding to throw the match to another event or just cancelling it and making better decision in the fairness to the fans that make this sport what it is.