Listen, dude, what we are repeatedly trying to tell you: Those deals TAKE TIME. And absolutely NO ONE will even try to begin to talk about a deal until they know what your status quo after Brexit is exactly.
Which means in a case of "No deal!" you'll be standing with exactly that, namely "no deals", for quite some time until you can cobble something together. Which would also mean that practically anyone would be tempted to bend you over the table because in that case you'll be desperate for such deals. You will not be in a position of power in such negotiations.
I'm also pretty sure that Lithuania didn't have much in the way of airspace travel agreements directly after seceding.