Yes, Halsin will attack you in your camp along with some animals the next time you rest if he's still alive after the siege if you sided with the goblins, even if he was still locked up by the goblins and you never even met him.
And bringing Sazza to Minthara will cause the siege to start as soon as you talk to Minthara. That's automatically going to lock you out of basically everything in the camp you don't take care of right then and there while you are there, as well as everything in the Druid grove you haven't yet resolved if you side with the goblins (and a fair bit even if you don't, like the Shadow druids plot). So taking the logical route of finishing the quest your are on and talking to Minthara will lock you out of a ton of content. Ditto if you follow one of the other main incentives to go to the goblin camp and talk to Spike on Wyll's behalf (iirc you can also interrogate the prisoner even if Wyll isn't there or you haven't recruited him) Because Spike will tell Minthara on his own after the interrogation if you didn't kill him.
For this reason I usually save Sazza/Spike for basically last on my playthroughs, because you basically can't do anything in the goblin camp afterwards, and even a fair bit of grove content is unavailable even if you side with the Tieflings after that point. Heck. Even the purely utilitarian loss of access to the merchants at the two locations is incredibly inconvenient, since iirc you are left with Blurg+Omelum as your only permanent vendor options after that point if you sided with the goblins. (Zhents, Dwarven, & Duergar merchant are all themselves temporary)
Two of the main reasons to go to the camp/major items of content there....potentially lock you out of a huge amount of content with no warning. Imagine if just talking to Kahga triggered the Rite of Thorns or the 'Druids attack Tieflings' cutscene on your next rest or next return to the grove. Yeah, you technically have a window to run around and do 'everything' in the grove before that hits, but that's a very metagame-y solution to a problem that most players wouldn't know was coming, and I'm pretty sure that most players here are pretty thankful that there isn't a easily-triggered 'endgame' scenario in the grove that can be triggered by talking to an npc that all the other npcs point you towards like there is with the goblin camp.
