I'm assuming you're talking about Aponogeton madagascariensis? It should have a pink, double-spiked flower. If this is it, then here the deal: Most plants in the genus Aponogeton have a dormant period. They pretty much look like they're dying and don't do anything for a few months. Then they come back and grow like mad and flower, then rest again. People say that the plant dies after it flowers because they don't realize that it just went into resting. It is also a myth that cutting off the flower will stop it from going dormant.
Sometimes it can be hard to "revive" the plant. It must have stored enough nutrients to pull through. Kind of like hibernation. So your plant will probably do this in a little while. Whether or not it comes back depends on the type of care it had. Some people remove the bulb from the tank and store it in a cold, moist place in sand or soil, while other people just leave it in the tank. I have an Aponogeton ulvaceus that grew like crazy, then flowered twice, then went dormant. It is starting to send out new roots now, about 5-6 months later. I just left it in the tank, didn't do anything to it. Hope this helps.