The two exits that resolve the grove
The game asks you to tie up loose ends at a few region changes. In Act 1 the ones that matter first are the road to the Rosymorn Monastery Trail and the road into the Shadow-Cursed Lands.
The time-sensitive list names those two entrances, plus the Shadowfell, the road out of the Shadow-Cursed Lands, and the Morphic Pool, as popups that auto-resolve unfinished business.
Save the Refugees ends if you take either Act 1 exit. If Investigate Kagha is unfinished, the Rite of Thorns completes and outsiders are shut out of the grove. If Kagha's quest is done and the goblin leaders are not, the grove stays open and the tieflings are gone. The journal line the wiki records is: "We left without helping the tieflings. They'll likely die on the road." Finishing Defeat the Goblins and then taking the exit before the celebration long rest does the same.
Halsin dies in his cell if those exits are taken before he is freed. Karlach leaves if the paladins of Tyr from Hunt the Devil are still alive when you take them.
Timers that run on a rest
After you approach Waukeen's Rest, a long rest, a fast travel, or entering the Rosymorn Monastery Trail kills the trapped survivors, including Benryn.
After you speak to Nere through the rubble in Grymforge, he dies if you long rest twice, leave the region twice, or mix those two. The gnomes tied to Save the Grymforge Gnomes disappear on the same clock.
The Rite of Thorns is not on a long-rest clock. It completes when you leave the region with Investigate Kagha unfinished.
Withers still finds the camp
Withers leaves the Dank Crypt if you reach the goblin camp courtyard without opening the sarcophagus. He still joins camp. Missing the crypt does not remove respec.
Underdark or Mountain Pass
Those two exits are the roads compared on the route page. The beginner page is the short version for a first run.
Official site: baldursgate3.game.