Fast? The Wildrose Alliance Party contested 3 elections: 2008, 2012 and 2015. The Alberta Alliance Party, the first fracturing of the right, was formed in 2002, and ran in 2004 before merging with the new Wildrose Party. Overall, the right has been fractured for a decade (at least) yet that did not prevent the PCs from majorities until 2015.

The Liberal slide does little to explain the NDP rise given the NDP rose over 30% while the Liberals fell just under 6%. Nor does the fracturing of the right really provide much explanation. Reality is, many PC voters shifted to Notley, clearly not viewing Wildrose as a rational alternative and actually the Wildrose lost vote percentage. Combined, there was a swing of about 26% away from the right (PC & Wildrose). 

Nothing in 2015 can predict 2019, but the 'fracturing of the right' thesis does not really explain past results. 2015 might be just a blip like 1990 Ontario as people try on something different, but then again, it might not.