[sayde]

Originally Posted by itachi-san314

Spoiler for kubo says:

ulq is clearly dead. i had heard that kubo wanted to bring him back, but he so clearly died in the manga that it was impossible... just a rumor I'm sure but yea, I think it wouldn't make any sense to bring him back after that very definite death

If Kubo was feeling creative and determined enough, he could bring him back. I mean we know he could dissolve parts of his body into dust and then have it reform. We also know he's one of the few arrancar who's been conveniently fortunate enough to have healing based abilities such as instant regeneration. So the foundation has been set. For example, all Kubo has to do is expand on what's already been established by revealing his body to have an automatic & instinctive ability to protect itself by breaking down to dust and then reforming at a later time (somewhat similar to Mayuri's trump card). I don't think that would be all too surprising or hard to fathom. It also wouldn't be very difficult to explain how even Ulquiorra himself wouldn't know about this ability until afterwards if Kubo confirmed Ulq's first defeat ever to be by Ichigo's hand. But for better or for worse, Kubo didn't seem like he was anywhere's close to coming up with this idea. So for all intents and purposes, you're probably correct in assuming Espada #4 to be gone for good.