User blog comment:IamJakuhoRaikoben/Chapter 463: Black Carpet, Review./@comment-1776824-20151123213644/@comment-25111584-20151124063344

As Wrath said, Mavis does not for one moment believe that Natsu could die out there. At most, she thinks that he might get captured, completely ignoring the fact that his capture would be a far worse outcome than his death.

As for what Gray and Laxus could do, it's more from her perspective than out-of-universe. If she actually believes that Natsu can face Zeref and his accomplices in a head-on battle without dying, why would she believe that Gray and Laxus couldn't just hold-off the Black Mage and his Shield just long enough to escape? A battle to escape should surely be simpler than a battle to win, right? Especially when the escape route is completely clear. What exactly makes her have so little faith in Gray and Laxus as compared to Natsu?

In the end, everything hinges on the fact whether you think that she is willing to let the boy die due to his own mistakes. If you think she is, then can't really convince you otherwise as this is basically a matter of interpretation. As for me, as much as I'd like to believe that she is pragmatic enough to make such decisions, I'm certain that this isn't the case and this is just a matter of blind faith.