A certain type of Leave voter has been polishing their version of the Dolchstosslegende since about five minutes after the vote was announced. I think you are vastly overoptimistic in thinking that a second referendum would be accepted as legitimate, either. As such, I tend to agree with the Lib Dems.

I also seriously doubt that the Lib Dems have done this *because* they think it won't have to be carried out. Parties have policies that they think they aren't likely to get a chance to put into practice, but that they believe in all the time. The SNP didn't shut down in the eighties, did it?