Hello,

I noticed that after the pirate league is wiped out, Vaulter Corsairs can no longer attack enemy factions, effectively making one of their core mechanics useless late game.

Is that a bug? When I played without the Vaulter DLC I could use privateers all game with no problems.

Nope, it's intentional. If there are no pirates that can attack you, it'd be very obvious who's attacking you.

Fair enough, kind of weird though that you could do that without the DLC. Is it because of the pirate diplomacy mechanic?

Can the pirate league respawn at least?

They spawn 3 times per game, and once that ends they don't spawn anymore.