I guess that, if the member state really wanted to reverse the process, the latter case could be turned into a sort of "state of leaving the EU until re-accessi

I guess that, if the member state really wanted to reverse the process, the latter case could be turned into a sort of "state of leaving the EU until re-accession". So it could be agreed that technically, the Treaties would cease to apply at some well-defined point in time, but at the same moment they would start applying again. A fun question would be whether a re-acceding country would lose its current privileges and its opt-outs of the Euro and Schengen.