I want to talk about tempering

[Eisenhower]

One thing that I'm curious about, is whether Aether drained by Primals regenerates over time, or if it's gone forever.

It could be that aether once committed to a primal becomes incompatible with Hydaelyn. In such a case, the aether could very well disperse and exist but still deny Hydaelyn power. If the Ascian-derived summoning methods were part next-level plotting, it may also be the case that such dispersed aether remains compatible with Zodiark, should it (he?) ever need the aether.