It is the UFC's responsibility to put together their events. It is Jon Jones' responsibility to 1.) look out for himself; and 2.) fulfill the obligations of his contract.
It is not his responsibility to make sure that the UFC's events are able to go on as planned.
The UFC should have planned for this contingency. They have a 40+ year old fighter in the main event of an otherwise weak card. Do you think there's a chance he could get hurt? No, not at all. There's no way this fight isn't going to happen. Right ...
Any responsible business man would have planned for the possibility that Hendo (or Bones) would get injured and be unable to perform. There are a lot of things they could have done to make that happen, but it's not Jones' job to facilitate that if it's not in his contract and it's not in his personal best interests.
So what should they have done? Put it in his contract.Add a clause to the contract that, in the event of Hendo's withdrawal, Bones is required to take a replacement fight up until XX days before the event. Would Bones have signed that contract. Of course, if they paid him more -- perhaps up front, perhaps as 'hazard pay' in the event the clause is triggered.
This is Jones' job. He has no responsibility to do anything for the UFC other than fulfill his contract. If a fight is not in his best interests, the UFC can either make it be in his best interests, or they can do something else. But at the end of the day, it's their responsibility, not his, plain and simple.
I can't believe the vitriol with which he is getting trashed. Jones and the rest of these athletes put their physical well being on the line to entertain us and to make the UFC millions of dollars. They deserve more than a little bit of the benefit of the doubt when deciding what's in their interests.
And remember, you pay your dollars to the UFC, not to the fighters. It's the UFC's job to entertain you, it's the fighters job to do what the UFC pays them to do, nothing more.