Mythal's Revenge - who should be the vessel?

Well the former tends to diminish their idea of actions having consequences. It also leads to people objecting when those consequences are permanent, whilst others object when they are not.

As for the latter, Mythal's survival down to the present does add complications to how you deal with powerful enemies, although we already knew from the Arch-demon that this is a possibility. What I found laughable with Corypheus was everyone was puzzled how he survived when Leliana and Morrigan in particular knew about the Arch-demon, so was it such a stretch to apply the same logic to an intelligent darkspawn Magister?

The other problem is that Solas knew it was possible. He admits that he didn't try killing the other Evanuris because you can't be sure they haven't got a back up plan. So why didn't he use his extensive knowledge of the Fade to revive Mythal or at least make contact with her? Perhaps he did and ignored her advice about how to deal with them or she suggested a prison but it was his own idea to use the Veil to seal it off. Even if it took a while for her to recover herself in the Fade, Solas was dreaming away for millennia, conversing with spirits and watching what went on in the world, yet they never made contact in all that time? I find that hard to believe.