User blog comment:Miskos3/Fairy Tail 538: When the Flame Goes Out, Review/@comment-173.46.77.185-20170603030539/@comment-7418318-20170604182008

I could imagine that by eating and absorbing them, Mira could have replaced Zeref as the "power source" if you will and thus those inside of her might not be affected by Zeref's death.

But if any Demon escaped the scene before she got there, that Demon is most likely gone now.

Not that it would make much of a difference if they were or were not inside of Mira considering that we saw exactly two instances of her using those... that we barely got to see what Sitri can do and how little in-battle-screentime Mira has in general.