LibDem policy is to look at the negotiated deal and its consequenses, then ask "deal or no deal?" NOT meaning bad deal or appalling deal (jumping off the cliff to become an offshore tax haven for billionaires and forget everyone else). The choice should be "this deal or stay as we are with all the benefits of being in the EU?"
Theresa May has changed her mind about all sorts of things - IN/OUT, election/no election, various policies which were rubbish when UKIP or Labour proposed them but are now those of a "strong and stable Theresa May Team" manifesto.
If she can change her mind what is wrong with asking those who voted for a pig in a poke to think again when they are finally told what that vote could lead to?