This was a nice demonstration of using partition switching to solve the problem of "loosing" the previous version of the data. I suppose this solution would make a bit more sense if instead of doing a TRUNCATE they were only removing and rebuilding say the current month or year of data instead of truncating the entire table.
I think the real thing this story highlights though is that data cleansing IS THE MOST IMPORTANT and often least respected part of building a data warehouse: "To make a long story short, it turns out one of our suppliers fed us an invalid date value, which we failed to handle correctly, causing the ETL to crash." This kind of situation is usually handled by having an "Unknown" value in your dimension table, so that you always have something to link to your fact record, and then have some process, even if it is manual, to clean up the "Unknown" records later.
Of course, if you want to improve the life expectancy of your dragons, don't take them North of the wall where they could be easily attacked by the white walkers.