Jim, //There's no reason that this decision, or indeed any other decision, can't be revisited in light of what has happened since.//
But the LibDems aren’t ‘revisiting’ the question. They’re quite openly trampling on the result. Still, one thing can be said for them I suppose. They’re not disguising their betrayal under a plethora of disingenuous excuses.
Here’s a thought. You said elsewhere //If the Lib Dems win an election standing on a platform to reverse or Stop Brexit, then by definition that will have been arrived at by a democratic decision. So much, then, for "trampling on democracy".//
Take a look at the EU parliament where you’ll find that the largest elected group represents the Brexit party. That, by your definition, means that their presence is, as a result of a democratic decision, justified – hence you might say the question has been revisited. ‘Remain’ still lost.