I'm definitely hoping for the best. I really don't want it to look or sound cheap.
The live singing only shorted pre-production, which is where the songs are usually recorded for production. I don't know that it helps with post at all. I have a feeling there will need to be post overdubs for any number of technical reasons. If anything makes a loud noise during a vocal take, they'll have to dub it in post. And we're talking about battle scenes, tavern scenes, factory scenes ... all with potential background noises ruining audio takes. Even in a non-singing film with similar scenes, there would be extensive overdubbing in post to fix those issues. There always is.
Aside from that, the live singing will create many issues with audio editing, piecing together a vocal performance and a visual performance from many takes, and then mixing it all together. Actually, from a post standpoint, it would probably be easier to work with a pre-recorded audio.
As far as visuals, I'm sure they will have to "matte in" period buildings, skylines, and/or remove anything modern from any location shooting they do. Those are all CG visual effects shots. You would be shocked at how much CG goes into even a small romantic comedy these days. There's even things like "wrinkle removal" from certain stars' faces. (Trust me on that.) So shots you think look simple can actually take weeks to work on. There's also wire removal, if any stunts in battles require actors to be lifted off the ground.
Les Mis could potentially have all of these things going on. And with a very slim post production schedule, they aren't allowing themselves any breathing room. I guarantee you they're paying serious rush fees already to make this release date. They may even be utilizing two or three post houses to divide and conquer the work.
I don't envy anyone who is working post on this film with a December release and production just now starting in March.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22