Not really missing in Action, but they've been missing for a while now.
After the disaster that occurred, that lead to LS2, we haven't really seen nor heard anything about them.
There was that area in the Cristal Desert that we got in PoF, but it was not the zephyrites themselves, same with the holosmith using zephyrite crystals (which should be leftovers, from when they left the Cristal Desert).
I think that with their main mission over(?), they might disperse or go back to the cities, but we haven't even seen a single former one, not even an aspect master.
Where are they and what happened to the remaining ones?
And an extra question: Given their focus in LS2, the announcement of Elite Specializations for HoT, and their lore of their magic (originated from Glint's cristals) being very similar to Air Magic (of Elementalists), why wasn't the elite spec of Eles for HoT, Zephyrite?
I know zephyrites were a bit of an isolated group, not letting outsiders in, but holosmith managed to get some cristals of theirs, why couldn't elementalists figure out how to use similar magic?
At least they already had lore and a number of skills and effects (If you even remember Aspect Arena).