I'd love to see McGregor knock Floyd's head off, but as others have mentioned that won't happen if its a strait boxing match. I'd still probably tune in to watch though.
I'm not so sure Floyd doesn't need Conor more than Conor needs Floyd. I know that Floyd doesn't need the money and is 'retired', but who else could he fight at this point that he would bring in more than 1 milion ppv buys? Maybe if he fought Canelo again, but that isn't going to happen. I think he cares a lot more about his legacy than he lets on.
Conor has options, he does over 2 million ppv buys if he fights either Diaz, Khabib, Woodley or Ferguson. The UFC is trying to get in to Russia, could you imagine Conor vs. an undefeated Khabib in Russia? A bunch of drunk, rowdy irish/russian fans in an arena together.