There are no plans on some kind of penalty for destroy a Questgiver?, im not saying i want them to lose 30k of LP and XP, or a giant Ent in front of them to smash their heads. But maybe a debuff that makes the "Ancestral spirits of the Forest" get angry with them.
Now you chip speed its reduced by 50% for X time, or your chop speed its reduced, etc etc etc. This way at least its harder for them to destroy a questgiver (applies the debuff after 1 hit or 3 (?))