Most players would consider the outpost conquered once all the pillagers are killed, and the player has taken the loot. You can do the following once you have conquered it. You can just leave. Pillagers (including captains) eventually respawn.

How often do Pillager outposts spawn?

Pillager outposts are semi-rare structures, generating every several hundred to couple thousand blocks. This makes them rarer than villages but less rare than woodland mansions.

Do outpost captains Respawn?

Pillagers and illager captains don't respawn around the outpost.