I honestly think they will have to make it an interim title to keep mcgregor interested. He "always shows up" and it's not his fault these fighters keep backing out. I'm not saying I fully agree with it but it's not like an interim title hurts RDA at all, and if it helps keep mcgregor interested and on the card, then it might actually happen. The show must go on.
Now if they do that, I think you have to get a guy deserving like Ferguson in there. Hell even Alvarez would be an option. Personally I would love to see Conor knock out Diaz and I think he would destroy Cowboy's liver with spinning back kicks but neither of those guys are deserving a title shot, even if it is a fake interim one.
The counter argument is, if they are going to make a fake interim title, then why do they need a credible opponent? I bet Dana and mcgregor are gonna be arguing for hours on the phone about what the hell to do about this.