Actually, Celene giving up the rule of Orlais is probably the only thing that would redeem her to Briala, and is actually a sort of fitting penance.
Celene killed Briala's parent's to prove herself in the Game and help secure her rule-- openly giving up the Game and her rule, especially if she doesn't particularly think Briala will come back to but wants to try anyways would be a very fitting step.
And she'd have to show that she's giving it up COMPLETELY. Like, moving to Ferelden (since that is the place Orlais looks upon with the most disdain) under a false non-noble identity completely.
And from a narrative perspective, it's a nice ending to tie things up with, just as having a 'tragic lovers' ending is a nice, solid ending.
Of course, Gaspard is not exactly someone I'd like to see on the throne, as much as I like the idea of saving tragic lesbians. Mayhaps if there was a third option/pro-elf Celene successor once you remove her from her own faction.