There is a lot of ‘sky-is-falling-in’ rhetoric, but once it all calms down the UK will spend the next couple of years extricating itself from the EU.
Afterwards things will largely be as normal.
Things will find their equilibrium.
And besides, it’s not like being in the EU enhances ones military capabilitues…. after all, the EU is built for Germany & the Bundeswehr is barely capable of subduing a bus of school girls.