Who are the other two daughters?
Yavana may be not dead since she was a bunch of pink smoke(like Majin buu) who entered inside the dragon but frankly i'm start to become annoyed that some charaters have the luxury of this magical rebirth or plot armors while others have to die normally.
On WoT2 there's a section that speaks of Witches of the Wilds, in which it is mention that there ar rumours of Witches on Ferelden (Flemeth), Antiva (Yavana), Nevarra and even maybe in Orlais... however there is no further information of those two, as only the ones that we know got a codex entry.
I know revival may be annoying (overall on characters that are given a lollipop by writers and whose means of revival/ resistance seem lazy written) , but it's more understandable on a world with magic, but on a case like this, I wouldn't be annoyed as she got killed in three rather short comics, which is wasting a potential character (same goes for Evangeline and Renn, their involvement is still bigger than hers, though).
Morrigan wasn't set-up to inherit anything as Gaider said somewhere in the forum
Mythal could literally be inherited by whoever she chose even an elven beggar in some unknown alienage.
I think people should keep that in mind, no matter how much they have hinted that Morrigan is a special snowflake, things change (and Morrigan's behaviour already leads her to remain mundane) and not only stated things, even already established things can change, look at Star Wars, General Grievous
used to be a ruthless Jedi killer, Starkiller
used to be canon and Darth Maul
used to be dead.