OP, it's very hard to sympathize with the schedule change troubles you're having. First, and this seems to be a very important piece of the puzzle, you haven't addressed the questions about the BKK-SIN flight that was cancelled. You claimed in a previous thread (one of the multiple created over the same issue) that the 23:45 flight was cancelled, and you were rebooked to 20:00. Nobody here has heard of a 23:45 flight out of BKK - it seems awfully unlikely that SQ will have a regional flight arriving at 3am - so it really does cast your whole situation in doubt.

Second, you're conflating two separate issues here. A mysterious schedule change that doesn't make any sense, and SQ's bereavement policy with regards to the return portion of your ticket for which you've now no-showed.

Third, you might want to rethink your threat of suing SQ when, with all due respect, the very basis of your story is in question.

Does a cancellation of one leg allow me to cancel the return portion of my flight?
How long does SA take in making ticket changes?