The Meaning of Life, the Universe, and Everything.
Is it possible to stop pillagers from spawning at an outpost? I've killed all the pillagers including the leader but they just keep respawning. Can't find a banner anywhere on the tower. What needs to be done to stop the spawning?
I would first try completely obliterating the tower. Next I would cover the terrain in something that they couldn't spawn on. If not that, I would completely block/quarantine the area off. I'm interested to know what the actual solution is, these are just the ideas of a bored man.
Most-best - possible - use of Lava, ever..? The trick with Water-alone is they Seem to Follow me up to at least 100( 'ish) Blocks away (very roughly: Illager Patrols seem to stay-still and be-aware of me about 32 Blocks away; so stop-Patrol'ling onwards), once they've Targeted me.
I'd thought I could continue a Grass Path route within about 200 or-less Blocks of them (their Pillager Outpost, of Re-Spawning), Build a Bridge over the River which thankfully wrapped-around them about 120º (that's 1 /3rd of 360º of a full-circle), but even though the River slows them down (since an Update in the far-distant now past which Slowed all-Mobs including the Player a bit, in Water, dramatically), I Still have to move-away from them quickly, once I get-away on Land. And on Land it was impossible: so I'd only ever easily be-able to Build the Bridge from the "safe(R)" side.
I'd recommend what my plan was: Build "safehouses" (with Escape Tunnels, somewhat-more easier since now-at least Trapdoors and 2-high Fence Gates, one-Closes when-in the Block, makes one start-Crawling at 1-high; slower: but less- Digging /Mining, to Build one, going-sideways [dunno if we can Crawl-Jump, haven't tested-fully to go 1-Block high while-Crawling]). Join them up (that's how I'd Build the Bridge, which might as well be an Underwater-too Tunnel, at that point meh, "Pillager Outpost, 'Chunnel'"), and gradually find-where you can Build a Wall in-between (find their Spawn-Range from the Pillager Outpost in the Wiki, it might be 64+ Blocks, dunno).
So Ring them in - at least - and then decide. "To Lava or not to Lava?"
Pillagers continue to spawn in a 71x71x71 cube centered on the pillager outpost. This means that they will continue to spawn even if you destroy the tower and waterlog the surface. They can still spawn in areas underneath the outpost and above the ground level if there are spawnable blocks available. The best possible solution is to remove all spawning spaces from the area. Either through TNT flying machines or slabs or water.
I have a tower that I turned into a farm so i can get Bad Omen whenever I need it. I restricted the spawning spaces by slabbing an outer ring area around the original outpost.