I think its worth a go just planting it as usual. You must of liked the look of it, so just enjoy it while you can.
Ive had a couple of non-aquatic plants in my tank before and they actually started to really thrive. It threw down some roots, but it looked abit messy so in the end I threw them away.
But if you keep an eye on it and it starts to rot, just pull it out and chuck it away. I personally wouldnt let it just float around on the top either.
Plants are something that often need to be replaced in an aquarium anyway. You may get sick of them or feel like redoing your designs.
My betta enjoys tall plants that sit just under the surface, he likes to lay on them and at night he sleeps there
At the moment I have a few hornworts - (ive attched a piccy of one). They are lovely and soft and look very pretty in an aquarium. They often dont produce roots (but a couple of mine have started to yay!). It grows quite easily in a variety of conditions, but the can start to look abit stringy if you have insufficient light.
Have you brought yourself any "plant food" yet?