So, backing up far enough to redo everything related to the Landsmeet, I was able to get almost everything I wanted, which included some benefits I hadn't expected.
Huge spoiler time obvs.
Reran Howe's estate to pick up the noble I'd missed and to do the surrender/escape properly. Hardened Alistair and pursued him all the way up to 'Love' (for the alternate version of the sex scene and also because I wanted to be *certain*.) Then went to Anora and promised my support if she'd marry Alistair and accept me as his mistress. She agreed. Then told Alistair to go along with it for political convenience, and he agreed. Talked the lady knight down at the landsmeet. Won the landsmeet vote, accepted Loghain's surrender. Alistair still starts to throw a fit but Anora snaps her fingers at him and he falls into line, unhappily - he agrees to keep his promise to her but refuses to remain a Warden if Loghain is one. Loghain goes through Joining. You then get one last chance to talk to Alistair at Eamon's estate. He's... not pleased.
PC: I want to talk about us.
Alistair: There is no us! There's just me and the woman who forgave the man who killed my brothers.
(or something like that)
So he breaks up with you and vanishes. BUT he's alive and not insane. Go through the rest of the plot and let Loghain sacrifice himself at the end, and then both Anora and Alistair are present for the final celebration. Since he's king, this time my PC swears she's staying around. Talk to Alistair at this point and he finds it fitting that Loghain died, says he's not angry with the PC anymore, and that they'll be seeing a lot of each other in the future.
So, they don't canon get back together, but a fangirl can certainly believe that the possibility is there.
ALSO, Anora+HardenedAlistair appear to make a very good royal couple, the kingdom is pleased. And (possibly because my elf said she was staying? or possibly it was a bug before) the elven epilogue went differently and better. Really, all my PC can regret about the outcome here is that she might have backed the wrong dwarf.