After a year and a half, and 45 sessions, my party has completed Descent into Avernus. AMA
We ran on the 2024 ruleset, and I used the Alexandrian Remix pretty much to the letter. Our party makeup was a Berserker Barbarian, a Spell fire Sorcerer, an Open Hands Monk, and a Gloomstalker ranger. We also had a druid/cleric multiclass, but the player moved away so we wrote an ending for that character. The finale was at level 13.
In the end, my party redeemed Zariel. They teleported into Elturel after retrieving the sword of Zariel, and sent one player with the rods to unlock the companion. They decided that sundering the chains would be too challenging a task as they had a target on their back from Zariel (thanks to some history between the Barbarian and Zariel herself, some past life shenanigans where she was one of the OG hellriders that died in the battle of Avernus) so they opted to try to fight Zariel directly. I had it so they had to deal substantial damage with the sword itself before they could get pulled into the last "memory dive" to redeem her - as they've been itching to fight Zariel the whole campaign. That, and a vow of enmity from Zariel towards the Barbarian would've made negotiation hard.
Picking the fight with Zariel immediately meant she called in her pit fiend, as well as the horned devil and Erinyes she had guarding the companion, in to assist her. They opened the companion with some smart moves. Especially once they summoned Gargauth to their aid (they rolled two nat 20s when persuading Bel their plans were solid, so he freed Gargauth and made him their body guard for this battle), they were holding their own. Zariel made a point to separate the Barbarian with the sword from the party, but the sorcerer managed to catch up. The Barbarian discovered quickly Zariel has pretty weak con saves, and used that to keep her blinded so she couldn't teleport to keep distance. Because of that, the sorcerer managed to catch up and keep the Barbarian healed while Zariel focused all of her attacks on her. Thanks to rage and fire resistance, she tanked her attacks pretty well.
Meanwhile, the monk, the ranger, and Gargauth, focused on the pit fiend, erinyes, and horned devil. In hindsight, I wish I had thrown another pit fiend in there to even the playing field a bit, but I was worried if they failed redeeming Zariel things would have gotten dicy.
They killed the pit fiend, horned devil, and Erinyes, with the monk and ranger dangerously low on health. Zariel downed the sorcerer in one turn, and the Barbarian caught him before he hit the lava. They retreated, and healed the sorcerer before Zariel had another turn. He used all 8 charges to destroy his healing staff, upcasting mass cure wounds to give the whole party a second wind. Zariel still had about 180hp left, and was going to call the remaining devils on the battlefield to her aid - and finally, she downed the Barbarian. She took the sword, which pulled them into the memory dive. I allowed the Barbarian to speak to try to persuade Zariel to choose a different path, but every time she offered up something, she had to make a death save. With one failure, and then three successes, she was stabilized. I wanted to raise the stakes at this moment, especially as the party has been a thorn in Zariel's side throughout the campaign, on top of the personal history. I made the default wisdom save DC for Zariel's choice 25, and if enough of the party passed persuasion checks, that was lowered to 22. Three of them surpassed 20 on their checks, so I also granted Zariel advantage. She rolled a 7 and an 18, meaning she accepted her angelic spark once more, and sundered the chains, helping the god who was imprisoned in the companion (more homebrew stuff tying in a PC backstory) lift the city from the Styx, and shifting it back to the surface.
Asmodeus shows up, to arrest Zariel, and to promote the Bhaalspawn who has fulfilled their fathers contract. They said their goodbyes before accepting a plane shift back to the material realm, and the Bhaalspawn had their body taken over by Bhaal, who will be the new archdevil of Avernus.
All in all, it was a solid campaign and my players loved it from the start. We ran 45 sessions, most of them 4-5 hours, but a few climactic sessions ran 6-8 hours. I'm running an epilogue/interlude session next which will carry us into Vecna: Eve of Ruin - as I've been building towards that in the background of the entire campaign.