I mean, could a divine class lose access to its divine powers if the (good) god was in opposition to the 'patron'-type relationship she had with Zariel (an evil aligned fallen celestial)?
As far as i know, it is possible to loose your acess to divine magic, if you upset your deity ...
Such feature is not present in BG-3 ... even tho i believe it would be at the very least "possible" to implement. (Wrote a suggestion some time ago.) :-/
But if we put aside the fact, that this is exactly something DM would need to decide ...
Personaly i would not expect that to be a problem ... i mean she had no choice, but to serve Zariel, and she run away ... that alone should proove to that Deity that there is no desire to return under her comand.
But yeah, fylimar is right ...
I see Oathbreakers as something like Warlock focused on meele in heavy armor.
But its not exactly corect: http://dnd5e.wikidot.com/paladin:oathbreaker
