Are you certain it was actually Green Wendtii? Both the red and green Wendtii will grow green with large round leaves when grown emersed, quite often this is how you find it in the pet store because its easier to mass produce this way.
When grown submersed, new leaves will grown long, narrow, rippled, low to the ground and brown (if using the red variant, otherwise they may be reddish as they are new but turn green quickly, many green plants do this)
The leaves dieing off is known as crypt rot or crypt melt and is completely normal when the plant is moved, the plant will not die.
emersed red wendtii (left)
submersed red wendtii