We do have to remember, even if Steven Harper wins a minority and the Liberals, NDP and Green don't cooperate to beat him, all three of them are on the record in favour of Electoral Reform. So they can pretty much just tell Harper to screw off, get their committee and then change the system all while Harper is stuck kicking and screaming.
They can still vote down any bill the Conservatives pass, and the parties can still work their platforms to restrict the PM. If Harper is stupid and tries to confidence every bill again, they can then go ahead and come up with a formal 'coalition' with which they could go to the Governor General with.
At this point the Conservatives have gathered too much bad will and if they don't win a Majority, they will just be walked over and ignored come time to vote on bills.