You may have been as confused as I was.
Why, given Harper's known inability to take orders or suffer any form of supervision, would he opt to remain a sitting Member of Parliament, now relegated to the opposition benches.
This is a guy, who during his concession speech, (which was a hastily re-written victory speech), didn't have the conventional decency to state his intentions to his audience before he scampered off the stage. His intention to resign as leader of the Conservative Party came via a statement released by the party president, John Walsh and even it was a rather muddled sounding bit of poli-speak with all the clarity of a cold latte. Conservative MPs have no idea if Harper is their leader.
What did come out was that Harper would continue to sit as an MP. And one doesn't have to dig too deeply to understand why.
The Duffy Trial.
As long as Harper is a Member of Parliament he cannot be compelled to testify as a witness in any civil, criminal or military proceeding. You can bet he'll be hanging onto that seat until the Duffy trial is concluded.