The link here is not specifically about sound design in film but about how sounds get patented and are linked to certain products. I found it very interesting as to how a sound can remind us of something or make us do or buy something. I thought you might enjoy it. A neurological sonic trip.
I realize this is an old thread, but iZotope RX3 does a great job of this if the music is in stereo. What you can do is use the Center Channel Extractor in RX3, and it will use phase cancellation to isolate the mono dialogue from the stereo music. I work in a trailer house where we frequently need to clean up bites from movies with bad stems.
Yes you should always use the boom as well as a lav, as the lav mic could sound crappy and if that's all you have then you're screwed.
It could fall off, scratch against clothes, get wind noise, lots of things, but if you have a boom over the top then you're covered.