Do really think the EU will let you leave without war?

Yup. We have a nuclear weapon and a permanent seat on the UN Security council.

Further, most Europeans skimp on their defence believing that someone else will defend them. At the moment, while the EU is trying to "punish" us, they're also begging us to send troops and planes to patrol the airspace of eastern europe which is being breached by unauthorised Russian aircraft. Sort of "We'e going to punish you, but please can you help us". You couldn't make it up.