You do realize that De Beers has gone in relatively aggressively on lab grown diamonds, in contrast to some other producers. This is more market research for them than trying to protect a dying business - their lab grown diamond brand is focusing on cheaper 'costume' jewelry rather than engagement rings, the big driver of traditional diamond sales. And this decision is partly a business one (they want to keep the cachet of an expensive and hard to source diamond ring and all of the commitment this implies) but also a realistic one - consumers couldn't care less about getting a 'fake' diamond for lots of costume jewelry, but haven't yet been convinced that it's as impressive to get it for something important.
I looked hard for lab grown gem quality diamond engagement rings when I shopped for my wife back in ~'08, but they didn't really exist in any substantial number/size (nor were they all that cheap). But I'm an exception because I attach no sentimentality to a 'natural' or 'unique' ring, I just wanted some shiny bling to make my girlfriend happy. Others take longer to be convinced, and De Beers isn't being stupid by doing their research.
I suspect that long term they will become a dominant player in the lab grown market and try to control the price of stones in such a way that the luxury premium of a 'real' diamond will still give their traditional mining business some revenue. But they are no longer shunning the space entirely; they're just trying to coopt it.