If I split the movie in two discs, what will happen when I click in the menu a chapter that is not included in that disc?
The next available chapter will be played. For example, you removed chapters 1-12 and you select chapter 2. Playback will start at chapter 13.
If no chapter is available, the playback of the title will end immediately, and you are usually sent to the root menu right away.
Using the example above, if you have splitted and kept the menu, "Play movie" will start at chapter 1 and end after chapter 12 on disc 1. It will start at chapter 13 and play until the end on disc two.
Hint: Try it. It's cool!
Save to files and play with your favourite PC DVD Player Software. If you like the result, burn to disc using the third button "write existing data".