@barnee
If the Capital falls the game is most often over - even if the Capital is re-captured - since there is no money to purchase new units - so the Capital would eventually fall again.
Concerning Sealion:
We have a German Strategy for the Sealion that involves German Landing Craft units.
Even when the Germans put everything in their arsenal for Sealion, the UK player would be able to defend against the invasion - since the Home Defense rule and the Bristish 1st Tank Army would be ready for defense in Late 1940 or Early 1941.
The UK player also has an option to place Mines in United Kingdom - this would reduce the effectiveness of German Landing Craft units.
Remember:
If Landing Craft units attack across a sea zone, this sea zone must be clear from enemy surface naval units from the start of the turn.
In other words:
A single UK surface naval unit would prevent the German Landing Craft units from attacking…
We haven’t seen a UK Flak Tower yet - due to the scenario described above.