I think you'd have to ask McGuigan that one. Although it must haunt you from time to time, other boxers have been known to hold back when they've had a previous opponent pass away in the ring.
Yeah. It's of course pure speculation but it sounds a bit like it. One would have to study all the fights and whatever else available to get a better picture tho... without getting a conclusive answer. And no, I wouldn't ask him. He's probably buried it as deep as possible.