> if the EU comes back with a substantial offer of change including a significant compromise on free movement

That's not going to happen - not because of the "gooodbye" rhetoric, but rather because freedom of movement has been embodied as one of the core principles of the EU. Free movement of goods and people are inseparable. This is even laid down in the bilateral agreements with Switzerland and Norway. The Swiss just tested the waters with the latest referendum on curbing EU-immigration but they haven't followed through. The EU has drawn a line in the sand here and I seriously don't expect them to concede this point.