Canadian leaders have always stayed too long. Because the choice to stay or go is left entirely to them. Compare Mulroney to, eg, Thatcher.
One thing I'd like to figure out at some point is how often — if ever — a parliamentary party leader has survived and succeeded in the wake of significant rebellion.
Leaders always try to hang on. But my hunch is the number who've a) survived and b) subsequently succeeded is... vanishingly small.