User blog comment:B214/Chapter 500: Fire and Ice/@comment-4933386-20160905123447/@comment-7418318-20160905133329

Considering Invel's magic couldn't even detect that Juvia wasn't really dead I'm surprised it kept Mavis at bey as long as it did...

As for the Strausses I think Ajeel is playing with them and that's how they could still be alive.