Yeah, I'd say there is a 0% chance they were lying about what happened with Snyder's family. There are about a million other lies, ones that are less horrific and aren't easily disprovable (seriously, it wouldn't be hard to figure out if they were lying about this) that they could go with if they wanted to kick him off the movie without being blatant about it. That said, is it possible Whedon is doing more extensive changes then originally thought now that he's there? Its definitely possible, and the change of composer is a point toward it. It wouldn't be a huge change to the core of the movie because they don't really have the time, but I could see Whedon still doing a lot of stuff for scenes like character interactions and things like that. I doubt the main plot of the movie would or could be effected, but he could definitely be adding things that would noticeably change some elements of the movie from what Snyder did. I hope that happens, but I'd say its probably about a 50/50 chance of it happening at this point. At the bare minimum I'm sure the movie will be at least a bit different with Whedon finishing it, but how much will be hard to say until the movie comes out.