I don't think anyone believes that superman will stay dead. And I keep bringing up Thor as an example to make my point.
Everyone knew that Thor was going to find a way back to Earth at the end of his first solo film in order to become a part of the avengers. But due to him having lost his normal means to Earth, it wasn't until near the midpoint of The Avengers that he showed up, which significantly limited his interactions and role in the film.
I fear the same will apply to superman if we have to wait until JL to see him resurrected. Furthermore, I'm pretty sure that they'll have to devote more time in showing on how he was revived and can't simply chalk it all up with a single passing line as Loki did with Thor's return.
I might be getting the wrong impression here but it seems like everyone here would be okay with just having superman return in JL to give some motivating speech to the group and he told involved in the final act, without having anything to contribute to the group in the previous two acts of the film.
Honestly, I wonder what goes on in Snyder's mind because he keeps saying on how the end of BvS gets the stage set for jl and yet if you end the film with superman dead, then how the he'll does that stage the DCEU in the right direction?