Any agreement between the UK and the EU that’s along the lines of May’s latest deal has no legitimacy or moral standing whatsoever, and should be considered null and void. Even if Parliament votes for it.
The referendum result was that we should leave the EU, not become more tied to it. That was the instruction from the people. What’s more, in the last general election both the Conservatives and Labour stood on a platform of implementing the result.
So they have no authority to make any such agreement in the name of the British people. They do not sign it in our name, and we shall not recognise it.