Ideal Scenario for the Ice Dragon:
Negotiate with the dragon and have it agree to swear to be one of Belegar's "Thanes" (we just established precedent!) with Zilfin as its territory, a lot of authority within that mountain, and permanent right to its lair there as long as it retains its office. The benefit to the dragon is that it can access stuff like entertainments and goods and people to bring it news and otherwise live a more interesting life than squatting in a dank hole for 99% of its time with absolutely no intellectual stimulation.
In return, it agrees to serve in Belegar's military against his enemies and maybe even let some dashing warrior ride it if they're into that.
On the dragon's treasure hoard, the dwarves can take anything that is "unmistakably dwarven"; that is, items with runes and manufacturing marks and such, but the chain of province of stuff like raw gold and silver and coins is considered broken... maybe most of it was originally stolen from K8P but at least some of it might have been seized by travelers and traders and other sources and over 3000 years who can say for any particular coin? Dwarves compensate the dragon for "recovering" thier lost treasures for them.
Like I said, that would be my ideal "Natural 100 Critical" result on negotiation.