I'm pretty sure the Civil War settled the question of whether or not states were allowed to just pick up and leave the Union.

And I can't actually believe this is a serious measure in Vermont. At least not without seeing some argument on things like food production, import/export ratios, public funding and so forth that implies that Vermont could sustain anything like its current prosperity if it were not only seperate from but also competeing against the States around it.
Maybe they could be self-sufficient; but I doubt it.