This is one of the unfortunate downsides to the hobby, compared to them being in their natural habitat. Out in the ocean, they will find a new anemone with easy, in captivity, you can pretty much forget it if one of the nems dies or dissapears, as you cant buy them....
As you mention Tranc0Fusione, its very common to see these in the LFS's with no anemone(s) attached because the nems usually die off in transit...