User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-1359322-20151207213203/@comment-71.50.115.82-20151208001936

Mashima did hinted of the dragons being a significance to Layla's death which is the same year the dragons "disappeared". The whole Eclipse incident may be the reason why she fell ill and therefore died.