As countries evacuate their embassy personnel from Afghanistan by helicopter, I'm wondering what would actually happen if all of Afghanistan's neighbours deny use of their airspace for these flights. There are six countries: Turkmenistan, Uzbekistan, Tajikistan, Pakistan, China, and Iran. Presumably the evacuation flights will have to cross one of these countries, and presumably these countries can deny permission.
If they all deny permission, then there's the further question of "how does one get the personnel to the embassy in the first place?". It sounds impossible for landlocked countries, barring some science-fiction style drop from space beyond the Karman line.
If a landlocked country's neighbours all deny passage, how can a country nonetheless operate an embassy in the landlocked country?
A historical parallel that comes to mind is the Berlin blockade. However, I can't find any details for why the Soviets didn't deny its airspace to the Allies, or if they did, how the Allies were able to fly through that airspace.