Some Aponogeton sp. are from places with wet and dry seasons, so when the plant goes through a climate change (or sometimes for no reason at all), then it can go dormant. All the leaves fall off and it's dead... but then 6 months later it starts to regrow! There are sites with instructions for "hibernating" them too, in wet peat in a closet or something along those lines. I don't remember the details since I've never done it - I tend to just leave 'em there and wait for them to bounce back.
So don't worry - I'd be VERY surprised if you killed it. Apons are quite hardy!
So don't worry - I'd be VERY surprised if you killed it. Apons are quite hardy!