What is the difference between "falis" and "faliĝis"?
I think because "falis" already in intrasitive (doesn't need a direct object) that you don't need to add -iĝ-.
That sounds pretty good, thanks
One wouldn't use faliĝi. It wouldn't have much of a difference from fali. Actually, you might argue that faliĝi is the same as ekfali and thus means 'to start to fall'. But it's usually not used like that.
Can one say "maliĝis" instead of "disiĝis"?
Not really. That would mean something like "to become the opposite of what it was before". I've never heard that word used before, and I'm not sure if it is understood in that meaning usually.
Could 'disassemble' be an accurate translation for 'disigxi'?