User blog comment:IamJakuhoRaikoben/Chapter 412: Dance Unto Ishgar, Review./@comment-1359322-20141208144403/@comment-9595671-20141208150827

I did have the idea they may have never actually died, remember the Dragon Slayers couldn't kill the weaker dragons in the Grand Magic Games so its possible Weisslogia and Skiadrum had to fool their sons that they had died.

Since Igneel was inside Natsu, both Sting and Rogue could have used an attack that was able to give them the opening to have them get inside Sting and Rogue and it also made them believe as a result the killed them.