I've run into this weird issue. I found him, had already killed 2 of the 3, killed the 3rd with him, and he went off to the grove. I fought my way out and ported over to go talk to him, but when I start walking down the stairs, their is a big battle going on where all the druids are killing him. Maybe this is meant to be, but it really feels like this isn't intended.
I believe the game has a "clock" but haven't confirmed it, yet. There's a time sensitive event in the underdark that resolved itself after I took a long rest so it's possible the same is happening at that junction.
I’m telling you it is the case. Time exists. I have 200hours into BG3 and sometimes if you don’t make it in time it’s too late. I’m sure there’s plenty of quests that wait for you but there are plenty that don’t.
In EA, I once killed all the Goblin leaders, went to where Halsin was being held, and everything was dead, and he was gone. Later went to the Grove and he was there, everyone was thanking me for saving him...
So things do progress behind the scenes, without your involvement.
I wonder if that's a timer or a trigger? Like, how is the passage of 'time' handled. Is it based on events (i.e. there's infinite play time but once all the leaders were handled the outcome is always the same giving the perception of time)? Based on rests? In game time passed?