I'm not sure what to feel about the former Justice Minister/Defense Minister/PC Party Leader. I don't think I've ever particularly liked Peter MacKay, and in some respects the guy was a bumbling fool; but like Flaherty, Prentice, or Baird, its possible he played some sort of moderating role or conscience in a Cabinet that many claim is dominated by the Prime Minister. Harper has lost so many strong voices this year that its beginning to become a bit sad; at some point, the Conservative government may truly become just the party of one man and his personal sounding board. That's a dangerous situation to be in for any government.
At any rate, I wish MacKay the best. Maybe he'll come back in a few years time, post-Harper, and run for the leadership of the Conservative opposition. Let's just hope he doesn't make any "promises" on mergers again.
As for his hypothetical Liberal opponent (or the revelation of Etobicoke-Lakeshore's Liberal candidate, Susan Watt, resigning), I'm not at all surprised. The downside of the push for early nominations is that you get people who like the idea of being an election candidate, but when push comes to shove they're just not up to the task. We had a similar issue here in Burlington in 2009, when we had a nominated candidate who then backed out when it became clear that there would be no election that year. Don't believe the nonsense talk of "rats fleeing a sinking ship" - all parties go through this, and its better happening now rather than a few days before an election call.