There are many ways to do massive damage in Baldur's Gate 3, we've learned. Players have devised an owlbear orbital strike and an impressively coordinated explosive barrel chain, but the greatest damage of all is hiding in your party just waiting for you to neglect it. Some early spoilers for Gale's storyline to follow, if you'd not guessed yet.
One of the first things that your wizard companion Gale explains about himself is that he needs to gobble up magical items from time to time, saying that there will be grave consequences if he doesn't. And should Gale die, a projection of him appears, with a warning to resurrect him within two days or terrible things will happen. He's absolutely not joking, and some players are finding out the hard way.
Reddit poster Namenotfound12 says they've been playing with a co-op partner who decided to kill Gale shortly after meeting him. "Some time later after 8 hours of playtime together, we get a cut scene of Gale back where we killed him, lighting up like a Christmas tree, and then proceeding to nuke our entire play through. Boom! Game over," Namenotfound12 says. They suspected maybe Gale was just obsessed with magical items and bluffing his way back to life, they say in the comments section.
They definitely aren't the only one who didn't buy into Gale's warnings. Skeeziksdt posted a video cutting together the same sequence of events: brushing off Gale's death, going on their merry way, and then seeing his body go into magical overdrive days later. "I thought he was fibbing," Skeeziksdt says, echoing the same assumption Namenotfound12 had.
I too have seen Gale's magical answering machine message after he died in one of my fights. He appears as a purple projection explaining that if you see this message it's because he's died and you need to revive him within two days, or else, with a laundry list of instructions on finding a resurrection scroll hidden on his person. Having already experienced death by failed skill check against a dying mind flayer within my first 30 minutes, I knew that Baldur's Gate 3 was not playing with me. I resurrected Gale immediately for fear of the consequences, so I feel quite vindicated that I was not overreacting.
Like other deaths, the world-ending magical nuke in Gale's chest doesn't actually roll credits. You'll just be prompted to return to a prior save due to your entire party (and the world) dying.
If you'd rather not deal with Gale's appetite for artifacts, you can just ignore pulling him out of that purple portal at the beginning of the game. After you've already recruited him though, best to keep a couple revivify scrolls on hand, just in case.