I dunno, I thought a lot of the rumours said WB used that tragedy as an excuse to get rid of Snyder. The fact that he didn't attend any of the premieres, still has never watched the movie they put out and has detailed how his vision was changed entirely speaks volumes. There is no reason they couldn't have delayed the movie until spring/summer 2018 to allow him the time to finish the movie properly.
If they were going to rush things just to meet that original release date the very least they could have done was stay true to Zack's vision for the movie. They changed almost everything by inserting all those Marvel style gags, removing his soundtrack and overall tone completely, cut out a lot of important scenes from Cyborg and Flash just to cut the running time etc. I think he has every reason to be disgusted with how WB treated him.
I do not pretend MoS and BvS had no issues, Snyder has always been a divisive film maker. I enjoyed those movies, especially BvS but no doubt they had some issues regarding script and pacing. They are though visually stunning, distinct in tone and consistent with each other. Green lighting JL then attempting to change tone three quarters of the way through production made absolutely no sense. They were never going to win over the haters, all they succeeding in doing was alienating the fans who enjoyed the previous two movies.
I completely agree that WB's decision to change course made no sense (especially that far along in the process), and they compounded their mistake by asking Whedon to rewrite & reshoot so much of the film and still hit the same deadline. And to top it off, I've read that WB proceeded to interfere with or reject several of Joss's new scenes as well. It's a miracle the movie ended up being even somewhat coherent.
I'd like to think that even WB wouldn't stoop so low as to leverage a child's death in the ouster of an employee. More than likely he was already feeling like a lame duck when they brought JW in to "help" him with rewrites. Even if they were best of friends & had a great working relationship, he had to feel insulted to be told to go back to the drawing board at that point. So when he stepped away for his family, there was likely little motivation for him to come back.