I've thought about it quite a bit and here's some additional variations I'd suggest:
If you manage to complete Act 2 with Gale's approval high without using his...
Scroll of True Resurrection
...and you have Dark Urge and/or Karlach in the party, he will reveal that he has it and that it could be used to restore the Dark Urge's memories, or Karlach's heart. Provided, either would have to trust him enough to allow themselves to die first, and in Karlach's case she'd have to have the infernal engine removed post mortem.
However, his study of the Weave and a basic rudimentary knowledge of how the spell functions has indicated to him that the Netherese magic imbued into the tadpoles would prevent using it to resurrect them without it, as they would be considered part of that person's mind. While technically possible, they would be severely mentally degraded to the point of uselessness, permanently. Though he had at least considered it.
This will only come up if Gale is romanced and has not been led down the path to using the Crown of Karsus for himself, and it occurs after the encounter with Oren. Though regarding that...
If someone died to her on the altar, it's also an option to use it to resurrect them instead.
If the player is Karlach or Gale origin, he's also able to ask Mystra to remove Karlach's infernal engine and restore in its place a normal heart. Though Mystra will only do so if he uses his Orb to destroy the Absolute as she wishes, or is able to defeat it on its own and returns the Crown of Karsus to her. This is perhaps the happiest ending for her.
Elminster can be asked to fix Karlach's heart, regardless of the above conditions, and he will admit that it is within his capability to do so; however, Mystra has forbidden his intervention in such a way.
Mizora can be asked, though Zariel has forbidden it regardless of the delightful price she can personally think of asking for in exchange.
Shar can be asked if the player is Shadowheart or Karlach, and Dame Aylin was slain and Karlach was romanced by Shadowheart (regardless of which of you is her). Shar will facilitate this after she has completed the task asked of her, though all of her love must be for Shar alone. Bittersweet, but Karlach's savior nonetheless.
Dame Aylin can be asked, though Selûne will grant Karlach a new life within her divine realm, the Gates of the Moon, within the shining silver hall of Argentil, at her Twilight. That will happen in the epilogue when she would otherwise burn up. Though it can only be asked of Dame Aylin after siding with her against Lorroakan. It's somewhat bittersweet as well, as she has to leave Baldur's Gate ultimately. Though she does later gush about how nice it is in the later epilogue. Though she's an Aasimar like Dame Aylin, albeit with her original face shape and hairstyle but with silver hair and ice blue eyes. One of her better endings, all things considered.
Vlaakith can be asked, though she demands you kill the one inside the artifact. And, well, considering it's a game over it's unclear if she ever had any intention of honoring it.
Raphael can be asked, though he requests the Crown of Karsus. And the heart's restoration is only to be delivered upon the delivery of the Crown. He does, however, make good on his deal, provided Gale hadn't been convinced to use it to become a god instead. He'll even give you the Orphic Hammer upfront so you can free Orpheus if you'd like. It's perhaps one of the happiest endings for Karlach, provided you're willing to accept what the heck Raphael is going to do with it.
If Gale becomes a god and Karlach is still alive he can be asked to restore Karlach's heart—and does. No conditions, no hoops to jump through. Just at a snap of his fingers. Though if the player is Karlach and romanced him, he will of course ascend her to become a goddess as well if she wants that. Whether Karlach went with Wyll, alone (if she's the player), or with the player, it results in a fairly happy ending for her. There are even romance scenes with her after as an additional bit of epilogue if she was romanced.
The idea is that it respects player intelligence that they'd at least try to ask some of these, and lore, but putting conditionals on most of them so most won't be encountered on most runs. But in existing they'll reward players that are clever or met certain conditions, or are willing to pay the price. Plus with Elminster, Mizora, Vlaakith, and Raphael all able to be asked without conditions—regardless that three of those are dead ends—it at least will appear like you're at least able to shoot your shot and try. And you should be able to take Raphael's deal on nearly every playthrough, even if you wouldn't meet the conditions of the others, albeit with a price.
I had considered having the Dame Aylin one also being conditional on if Karlach is romanced or the player is Karlach on top of that as it might risk make giving her a happy ending too common. But upon reflection, you're already having to do three conditionals to get it: first saving Aylin, then informing her of Lorroakan, then siding with her against Lorroakan. Even if you do one of those you might not do one or two of the others.
That makes it so there's two options on nearly every playthrough, with at least one option at minimum (Raphael). If you have or are Gale you have 3 more options, though might not necessarily realize it and they're mutually exclusive but it does allow ways of stumbling into the conditions of one of them. And if you're an evil Shadowheart you have another option, provided you romanced Karlach. Though Karlach origin also gets an option if she romances an evil Shadowheart, but with a cost. But even Karlach with a good Shadowheart has an option if she plays her cards right. Everyone could technically get that option with the right choices, even if you don't have Shadowheart at all.
