You gotta think bigger. Death would be too easy for the dragons. Shatter their pride and drag it through the mud. Cut off their wings, seal their magic, and then force them to work in the restaurant serving humans and other races.
There's something I learned about getting salt from seawater if anyone cares. You do boil it to evaporate the water to form salt crystals. However you want to dump out the liquid when it's down to 20% or something because that'll have all the bad tasting minerals and literal shit. There's some...
He's got the backing of the kingdom, the princess, pirate waifu, loli vampire, and now the guild master. If she really is a good merchant then she'll know better than to mess with him. We'll have to see what happens.