As Dan pointed out earlier, there are a lots of conspiracy theories floating around about John McCain's surgery. Personally, I have trouble believing John McCain somehow suddenly scheduled a procedure - where someone is drilling into his skull - just to play games with a healthcare vote. Even for an obstructionist, that seems ...extreme.
However, I have no problem imagining Mitch McConnell taking advantage of McCain's medical issues and using them to buy a little time. If the surgery happens to fall on a date that gives McConnell an extra two weeks to save his failing healthcare bill, I'm 100% sure he's happy to exploit that. This is particularly true if he was certain he didn't have the votes needed to pass it this week.
According to Rand Paul the Senate Majority Leader still doesn't have his ducks in a row, so he's probably thrilled to get a 14-day reprieve.