I mean you're right.I think we have options:
A) A divine artifact that demons are weak against (I assume they exist in Prothea, we just haven't seen them yet). I can see securing or even creating this being a big plot point in the future
B) Andras recognized he could get killed in battle(and got hurt by a bow) so he can get ganged up on by an entire army loyal to Rowan. I don't care how fast he heals, if we keep chopping limbs off something's gotta give.
C) Drop a really big rock on him, I don't know.
Andras is prideful and easy to goad into a bad fight or at least into staying in a battle that is turning against him. I honestly think Jezera is more dangerous. The moment she thinks things aren't going her way she is gonna teleport away with some BS magic artifact and will be trouble down the line. She needs to be caught completely by surprise which is of course hard as hell considering her proclivities.
But also, rule number #1.
Porn game.
Jezera is hot. There will be some McGuffin or technique Rowan will get to neutralize her but keep her around as a fuckpet. Or maybe turn her "good" or something.
Just something to neutralize her as a threat but keep her juicy purple ass around.
I'm also sure it will be written more eloquently and with more build up, but there will be a way to deal with her and fuck her.
Gay side, I'm sure there will be way to do that to Andras too and keep him around as a bottom for role reversal.
But considering that the majority of users tend to be straight (I'm imagine) there will probably be some way to yeah, goad him into a losing battle that takes his life.
Helyana's Bow hurt him. Chop off his head, that's all it takes.
Or chop it off then burn it or something.