Getting back into the EU means joining the Euro. If it's possible to cancel Article 50, then that's viable and can be sold to the public. But joining the Euro is economically insane - unless you plan to have a much larger EU budget and use that money to make large economic transfers between the member states.
The current EU budget is about 1% of EU GDP. In order to make the Euro a viable long-term currency that's got to be increased dramatically, to something like 10-20% of GDP, and large chunks of it spent in the regions of the Eurozone that are suffering economically at that particular time. You can cut that amount by having schemes like jointly issued government bonds and a well-enforced common banking supervision and bail-out system - and obviously a large chunk of that spending could be common unemployment insurance - so it needn't require the EU to become the state and the countries just regions. But it definitely means much more political integration - which isn't even popular in the countries like Germany where a large minority of voters actually believe in a federal EU - let alone Britain.