I was actually more sad at Juvia's "death" than at this even though I knew she was going to come back but maybe that was because I never really cared about Makarov. Also, why couldn't they have used Mavis' plan? Until I know how her plan would have turned out I will see this as an unnecessary death.
The battle between gray and natsu stop to figure out what happened, gray sees this oppurtunity and strikes natsu with a ferocious blow. Thinking he killed him, Natsu fully awakens as a dragon.