I came to know that those who completed the summer nyxmare rescue hard path got the artifact but not the raven dragon i.e, the heroic boss at the end

This means only one thing.....

Raven escaped and WE ARE GOING TO HAVE ANOTHER RESCUE!!! Of course Deus is freed from the spell.

I'm fine with the rescue if we need LoD dragons and of course huge improvements in the rescue.

But if we need new dragons,.... Well I can say only 2 words:- we're dead.

I am not sure Raven escaping means another Rescue or if he will be in another story. After all he could just be in a race if he was heroic. I don't remember looking to see what his rarity was.

Most likely we will get another story, not sure what format it would take but here is a hint.....every story has had the introduction and requirement of it's own dragons.