Recall in Star Wars: Empire’s End issue 1, the Emperor blows a gasket when the initial firing of the Galaxy Gun does not go as planned. This in turn reveals his fraught deteriorating condition of his final clone body.
This causes the Emperor an immediate emergency to quickly get some spare bodies.
He then goes to Ossus to harvest some Force-sensitive Ysanna to serve as immediate replacement bodies.
They included a unique special feature different from what was done with, say, Han Solo:
That’s our secret, Skywalker. Only the Emperor can unfreeze your friends.
Unfortunately, the Emperor meets an untimely death. There was no indication, and in fact, generally impossible circumstances for Skywalker to have obtained the secret to freeing the Ysanna before the Emperor’s death.
And in any case, he ultimately dies a final death under any circumstance in canon in Star Wars Episode IX: The Rise of Skywalker, again without any indication in any post-2012 Legends continuity, that anyone bothered to remember to free Okko.
Is Chief Okko and the carbonited Ysanna still slabbed in carbonite?