ToME: the Tales of Maj'Eyal

So for my next win I was thinking I want to try an Anorithil. If I drown High Sun Paladin Aeryn at the start, will she not be there in the final battle? I'd assume so, but I wanted to be sure.

Since no one else answered you, yes. Drowning her means she won't be there in the final fight. IT also means you won't need to speak with her to make the prides appear, they'll be available as soon as she's dead. Furthermore, since she won't be there, that also means you won't be able to get your shiny cure-everything talent from her, so you won't have that either.