The Lib Dems did come from Centrist Labour MPs leaving when The Militant Tendency group were strong and joining the Liberal party. What happened then was that the Moderate Left, under Neil Kinnock, took back control of the Labour party which led to Tony Blair's Land slide victory in the 90s.

Momentum has control of the party now, at the local level and at the top of the party tree. It's hard to see how they can be removed, unless they themselves acknowledge that their goals are unattainable and give back power to the center. If pigs can really fly like that, what will we do for bacon?