One day, when a Russian fleet sails around the western coast of Ireland and decides that it quite fancies stopping off and staying in Galway for a while, without your permission, on whose support will you look for ? Obviously not being in NATO you wouldn’t dream of asking them
So you think when Brexit happens that the British government will stop protecting the British isles and Irish waters including the Atlantic waters off the west coast of Ireland?
You realise that both the Irish and British government have an agreement for British support right? The RAF responds to air threats and the Navy to threats in the water. It's been like that for a long time and i don't see it changing.
When those bear bombers flew over Ireland by the Russian military the RAF scrambled. When those ships were awfully close to Donegal that one year the British navy and the RAF responded. There have been a multitude of cases involving support.
Britain would not want to be flanked by any threat to them also.
You scenarios are a bit mad mate honestly. You think they will rip up every agreement they have with EU nations currently? Isn't the point that your government wants to renegotiate and keep said deals but still exit the EU?