So...... definitely NOT in the camp about the death of Snyder's daughter as PART of a conspiracy ... simply a coincidence that might work out for the film (at least for some audience members).
I hear the idea that reshoots aren't a big deal...and I think SOMETIMES that is true...but also, just a few minutes of film, even WITHOUT big special affects can great affect how it is perceived. The last few minutes of The Last Samurai, where Tom Cruise is shown to have survived, basically ruins the film. Had he been the Last Samurai for a couple of minutes (before dying), it would have been a cool movie. But by that short scene, it becomes a perceived trope of Cruise being the super-hero of the movie, and loses my interest in it.
I think Snyder has done the same thing, with those scenes of Jonathan & Martha later in life...it totally takes away scenes when Clark was younger, and they showed real love and wise guidance for Clark.
With Justice League, I hope (and exect) Whedon will add or delete scenes which will make us "like"the Justice League, and hopefully feel like a comic book movie.
I would hope, with the grief he & his wife have to deal with, won't "claim his right" to have the movie he "intended it" (which is what I hear the Guild rules are supposed to ensure), but just let it go, and even if Whedon changes some major things of the movie, will just let it go, and be gracious in the final product. His leaving wasn't really predicated on disputes with WB -- it was personal. So I don't think he'll show bitterness, even if things are different than he initially filmed.