There is an interesting article from John Ivison in the National Post that I missed when it first came out.
Have a read of the article, and continue on after you've done so.
The claim in the article is that should MacKay become leader, the Conservative Party may re-split in two, the old PC Party and the old Reform Party.
It further implies that anyone from the old PC side could split the party should they take the leadership.
If I was a Conservative, I'd be highly offended by this. It implies that the party can only stay merged when half of it is subservient to the other half.
It implies that unless the PC Party does what the Reform Party wants, it will prevent it from ever getting in government.
I highly doubt this is the case. While there may be some in the Conservative Party that would leave, I can't see a radical change in politics. There are only a small number of options for those on the further right wing of the Tories
1 - Try to re-create the Reform Party. This new party would look an awful lot like a "Wildrose Party of Canada". Such a party would likely struggle to win very many seats, but could win a dozen in places like Alberta, BC and Saskatchewan.
2 - Join the Libertarians. This could gain some mileage, I could see the Libertarian Party, if it had sitting MPs, manage to at least re-elect them, if not gain; but fiscal differences between the wings within the CPC are just not that great.
3 - Join the Christian Heritage Party. While this party would be less successful at election time, it is more likely to see defections.
4 - The disgruntled MPs end up sitting as Independents.
Given this would mean destroying the Conservative Party, potentially preventing it from forming government, I don't see many MPs taking up this option, and if only a small number do, option 4 is most likely.