ending spoilers, in case anyone was curious

[biggest loser]

https://imgur.com/a/jFfajHR

I didn't expect anything unique to happen so I'm not disappointed-but not destroying the wyrmheart doesn't seem to have any dialogue or anything. The boss after the dark dragon is at its normal level instead of being level 99.

[Eddiero]

If you destroy the heart the dragon goes down to lvl 60 same as the following boss.