I have only been on one flight with mechanical problems, and that was x-HKG - lucky me!

We already boarded. I already had a glass of wine. Then came the announcement. Fortunately it was a 744 and we were in HKG. It took CX a short time to prepare another 744 for us to get on. There was only a 2-hour delay!! I can imagine what happens for another aircraft in an outpost.