We know that in churning mists, Tharl Oom Khash (if someone knows the translation please do) is suposed to be the place where Ratatoskr died.

Althou lahabrea is dead(he was ppretty much the cause of pretty much all summonings that we know exept.... In Ununkulhai quests(wich, name is one of the stars of the serpentarius constelation where elidibus that posseses the serpentarius stone in tatics, and taking in mind its garments and urianger filiation i would speculate that Ununkulhai is directly related to elidibus and that {totally speculating} Urianger summoned, or has something to do with the ravana/bismark)

In those quests he says that these new primals were not summoned like the others, elementals, from before. This may seem silly, but i think it would make sense that the new primal is Ratatoskr, the levin crystals (darkscale fates, althou he asks for nidhog power) nidhogg used only fire skills in its fight in the Aery.

I dont know, pretty sure the other dragons have knowledge of what happened to bahamuth and tiamat but still... SOMEONE could do the summon by themselfs. Cough, urianger.