Personally, I'd like to make it through my career without ever having to deal with that situation, but it sounds like 750XL handled them all with the professionalism and care one would hope to receive!
Fortunately, I'm only the monkey that meets you at the end of your flight and don't work on board, which is probably why I've seen a fair few deceased pax upon arrival.
One thing I have noticed is from my own experiences and my colleagues, is that each situation tends to be handled very differently depending on the airline, aircraft and culture of passengers. In each case, though, it's been handled as best as they can.
I did some work on cabin standards a few years back and I gather that some of the ULH aircraft that were coming into service at the time had a customer option for a refrigerated bay/drawer to keep a deceased pax. It only came up in conversation but it seemed to be a serious comment made by someone who would know.
I believe that Singapore A345 ULH aircraft have a 'body cupboard'!